This paper presents the bit error rate (BER) performance for various quadrature amplitude modulation (QAM) schemes with low-density parity-check (LDPC) coding using pilot symbol assisted (PSA) - extended Kalman filter (EKF) phase-noise compensation (PNC) in the presence of strong phase noise (PN) for orthogonal frequency division multiplexing (OFDM) waveforms in sub-terahertz (sub-THz) bands. In the sub-THz bands, PN is a significant hardware impairment and comprises random Wiener PN and uncorrelated Gaussian PN. Hence, in this paper, we propose a compensation method for the correlated Wiener PN by using PSA-EKF PNC and to make use of the large coding gain from the LDPC code to mitigate the effect of the uncorrelated Gaussian PN in the sub-THz bands. Based on computer simulations, we show that the loss in the required received signal-to-noise ratio (SNR) at the BER of $10^{-6}$ compared to the case without PN is suppressed to less than 1.0 dB for both QPSK and 16QAM with the LDPC coding rate of $R=8 / 9$ for the power spectral density level of an uncorrelated Gaussian PN of $-105 \mathrm{dBc} / \mathrm{Hz}$ or lower. We also show that the 64QAM scheme achieves the BER of $10^{-6}$ by utilizing the LDPC coding gain at the cost of an increase in the required received SNR in the presence of strong PN in the sub-THz bands.

This paper presents detection probabilities for the physical layer cell ID (PCID) in the presence of a large carrier frequency offset (CFO) and strong phase noise (PN) for the New Radio downlink in sub-terahertz (sub-THz) bands. In the sub-THz bands, CFO is large due to the frequency error of the local oscillator in a set of user equipment. The PN power becomes large because of the increase in uncorrelated Gaussian PN with high frequency components due to a significantly wide transmission bandwidth. We compare the PCID detection probabilities of PCID detection methods that employ two promising CFO estimation methods. Computer simulation results show that the PCID detection method using fractional frequency offset (FFO) estimation based on the autocorrelation using the cyclic prefix waveform and joint integer frequency offset (IFO) estimation with the primary synchronization signal (PSS) attains a higher PCID detection probability than that using FFO estimation predicated on the cross-correlation of the PSS and joint IFO estimation with the secondary synchronization signal (SSS) sequence in the presence of a large CFO and strong PN in the sub-THz bands.

The time-varying phase noise (PN) due to a local oscillator of a base station and a set of user equipment (UE) is a major impairment to the backhaul and access links employing millimeter-wave bands. This paper presents the bit error rate (BER) performance of a pilot symbol assisted (PSA)-extended Kalman filter (EKF) phase noise compensation (PNC) method that combines PSA PNC in the time domain and iterative PNC using the EKF in the 3rd Generation Partnership Project (3GPP) PN model for orthogonal frequency division multiplexing (OFDM) backhaul links. We first derive the discrete-time transfer function of the power spectral density based on the z-transform for time-domain 3GPP PN signal generation employing a small number of low-pass filter taps, and show the validity of the generated PN signal based on a comparison to the continuous-time transfer function that is specified by the 3GPP Technical Report. We then show that when using PSA-EKF PNC with a low-density parity-check (LDPC) code and the coding rate of 8/9, the loss in the required received signal-to-noise ratio (SNR) satisfying the BER of $10^{-8}$ in 3GPP PN Models 1 and 2 compared to that without PN is only approximately 2.3 dB and 0.6 dB, respectively.

This paper presents the performance for New Radio (NR) downlink initial access including physical-layer cell ID (PCID) detection, and demodulation and decoding of the physical broadcast channel (PBCH) payload using the synchronization signal block (SSB) in the millimeter (mm)-wave bands. In this paper, we take into account carrier frequency offset (CFO) and time-varying phase noise that are major impairments in the mm-wave bands. Link-level simulation results show that the detection error of the primary synchronization signal (PSS) has a large impact on the detection probability of the PCID, that of the PBCH demodulation reference signal sequence (DMRS), and on the resultant detection error of the PBCH payload. We also show that the residual CFO after CFO compensation affects the detection probability of the PBCH payload using Polar coding. We show, however, that the high detection probability of 90% for the correct radio frame timing based on the PBCH payload information is achieved at the average received signal-to-noise ratios of approximately -3 dB and -5 dB for the Tapped Delay Line (TDL)-C and E channel models, respectively, which indicates an effective SSB configuration for the NR radio interface.

This paper proposes a phase noise compensation (PNC) method using frequency division multiplexing (FDM) pilot multiplexing with high-order QAM in discrete Fourier transform-Spread orthogonal frequency-division multiplexing (DFT-S-OFDM) back-haul links. The proposed PNC method comprises pilot symbol assisted (PSA) PNC and iterative PNC using an extended Kalman filter (EKF) associated with the cancellation of distortion due to puncturing of the single carrier (SC) and pilot interference. Computer simulation results show that the peak-to-average power ratio (PAPR) at the complementary cumulative distribution of 10−4of the DFT-S-OFDM with FDM pilot multiplexing is decreased by approximately 2.7 dB compared to that for OFDM for 256QAM. We show that the proposed iterative PNC receiver achieves the bit-error rate (BER) of 10−8at a received signal-to-noise power ratio (SNR) of approximately 26.0 dB with 256QAM for DFT-S-OFDM. The loss in the required received SNR satisfying the BER of 10−8of the proposed iterative PNC receiver for DFT-S-OFDM compared to OFDM when both employ FDM pilot multiplexing is suppressed to approximately 1.0 dB for 256QAM. We conclude that the proposed iterative PNC with FDM based pilot multiplexing is effective in achieving a very low BER such as 10−8in DFT-S-OFDM backhaul links.

This paper proposes an iterative phase noise compensation (PNC) method using an extended Kalman filter (EKF) that employs pilot symbol assisted (PSA) PNC for computing the initial values in the EKF for orthogonal frequency division multiplexing radio backhaul links. In the PSA PNC stage of the proposed method, the phase noise is estimated and compensated using frequency division multiplexing (FDM) pilot symbols that are multiplexed into the data symbols. Based on the decision symbols after the PSA PNC, the time-varying phase noise estimate and variance in the time domain are tracked and updated using the EKF iteratively. The proposed method achieves a low computational complexity because low-density parity-check (LDPC) decoding is conducted only once after the phase noise in the received signal is suppressed by PSA-EKF PNC. Computer simulation results show that the loss in the required received signal-to-noise power ratio (SNR) satisfying the bit error rate (BER) of 10-8of the proposed method compared to that without phase noise is suppressed to within approximately 1.2 dB for 256QAM with LDPC coding at the coding rate of 8/9.

This paper presents the initial physical-layer cell identity (PCID) detection time or initial cell search time that satisfies the required PCID detection probability using the synchronization signal block (SSB) of the New Radio (NR) interface based on system-level simulations. We assume heterogeneous networks (HetNets) that comprise 19 macrocell sites consisting of 3 cells each with the carrier frequency of 4 GHz and 3 small cells within each macrocell using the carrier frequency of 30 GHz. We investigate the effects of the base station (BS) transmitter power, the number of antenna elements of a macro BS, and cell range extension on the initial PCID detection time. System-level simulation results show that an initial PCID detection time of shorter than 200 ms is achieved at the PCID detection probability of 95% in HetNets using 8 and 64 transmission beams at macrocell and small cell sites, respectively, for a set of user equipment employing 2-antenna receiver diversity.

In 5G cellular systems, millimeter-wave bands are anticipated to be deployed in dense small cells in heterogeneous networks (HetNets). In downlink initial access, the carrier frequency offset (CFO) that depends on the frequency stability of a local oscillator of a set of user equipment (UE) is the most significant impairment for a UE to search the physical-layer cell identity (PCID) of the best cell site. This paper presents comparisons of PCID detection methods with CFO compensation using the synchronization signal block of the New Radio (NR) specifications for millimeter-wave bands. Link-level simulation results show that the fractional frequency offset and integer frequency offset estimation method based on cyclic prefix (CP) correlation achieves a higher PCID detection probability than that based on the cross-correlation between the received signal and the primary synchronization signal (PSS) sequence replicas on the condition that the UE frequency stability is 5 ppm for the subcarrier spacing of 480 kHz at the carrier frequency of 60 GHz. Moreover, we show based on system-level simulations that both methods achieve the PCID detection probability of 95% in a short PCID search time of less than approximately 200 ms.

This paper proposes a physical-layer cell identity (PCID) detection method that employs joint estimation of a frequency offset and the secondary synchronization signal (SSS) sequence for the 5G new radio (NR) initial access with beamforming transmission at a base station. Computer simulation results show that by using the PCID detection method with the proposed joint estimation, an almost identical PCID detection probability to the primary synchronization signal (PSS) detection probability is achieved for an average received signal-to-noise ratio (SNR) of higher than approximately -5 dB. The results suggest that the residual frequency offset is compensated to a sufficiently low level leading to accurate SSS sequence estimation. The results also show that by using the PCID detection method, high PCID detection probabilities of greater than 90% and 50% are achieved at the carrier frequencies of 30 GHz and 50 GHz, respectively, at the average received SNR of 0 dB at the frequency stability for a local oscillator in a set of user equipment of 3 ppm.

This paper presents the sequences and multiplexing scheme for the primary synchronization signal (PSS) and secondary synchronization signal (SSS) using a single-carrier waveform for physical-layer cell identity (PCID) detection in systems beyond 5G. We first investigate the PSS and PCID detection probabilities using an M-sequence and a Zadoff-Chu sequence for the carrier frequency of up to 90 GHz considering the frequency stability of a local oscillator in a set of user equipment of approximately 3 ppm or greater. We also compare the SSS sequence detection method in the frequency domain based on the estimated channel response using the PSS and that in the time domain without channel estimation from the viewpoint of achieving a higher PCID detection probability. Finally, we investigate the effect of hierarchical SSS sequence assignment to decrease the computational complexity of the SSS sequence detection while achieving a high PCID detection probability for single-carrier waveform.

This paper presents the bit error rate (BER) performance of frequency domain equalization (FDE) using low-density parity-check (LDPC) coding for single-carrier line-of-sight (LOS)-multiple-input multiple-output (MIMO) multiplexing. We use partial LDPC coding with double Gray mapping and collaborative decoding, which is suitable for a high coding rate such as 0.9. Computer simulation results show that partial LDPC coding decreases the required received signal-to-noise power ratio (SNR) at the bit error rate (BER) of 10-7by approximately 1.0 dB compared to that for full LDPC coding for 256QAM in a Rummler fading channel. We show that the required received SNR at the BER of 10-7using partial LDPC coding is decreased by more than 6.6 dB compared to that without LDPC coding even for the deep notch depth of -20dB regardless of the relationship between the notch frequencies in the direct and cross links for 2×2 LOS-MIMO in a Rummler fading channel. Therefore, we conclude that FDE using partial LDPC coding with double Gray mapping and collaborative decoding is effective in achieving a low BER for single-carrier LOS-MIMO in microwave radio backhaul channels.

This paper presents the physical-layer cell identity (PCID) detection probability using the narrowband primary synchronization signal (NPSS) and narrowband secondary synchronization signal (NSSS) based on the narrowband Internet-of-Things (NB-IoT) radio interface considering frequency offset and the maximum Doppler frequency in the 28-GHz band. Simulation results show that autocorrelation based NPSS detection achieves almost the same PCID detection probability as that for cross-correlation based NPSS detection using frequency offset estimation and compensation before the NPSS received timing detection, while the former achieves a lower level of computational complexity than the latter. We also show that when using autocorrelation based NPSS detection, the loss in the PCID detection probability at the carrier frequency of fc= 28 GHz compared to that for fc= 3.5 GHz is only approximately 5% at the average received SNR of 0 dB when the frequency error of a temperature compensated crystal oscillator of a set of user equipment (UE) is 20 ppm. Therefore, we conclude that the multiplexing schemes and sequences of NPSS and NSSS based on the NB-IoT radio interface associated with autocorrelation based NPSS detection will be applicable to the 28-GHz frequency spectra.

This paper presents the physical-layer cell identity (PCID) detection probability using the primary synchronization signal (PSS) and secondary synchronization signal (SSS) for the New Radio (NR) radio interface considering the large frequency offset in the 28-GHz band. Simulation results show that crosscorrelation based PSS detection achieves a slightly higher PCID detection probability compared to autocorrelation based PSS detection in the lower average received signal-to-noise power ratio (SNR) below approximately 0 dB for the subcarrier spacings (SCSs) of 120 and 240 kHz. Meanwhile, the required computational complexity for the PCID detection of the latter method is much lower than the former method. We also show that when the frequency error of a standard oscillator of a set of user equipment is ε = 20 ppm, the PCID detection probability is decreased by only approximately 28 (22)% and 3 (6)% compared to that without frequency offset at the average received SNR of -10 and 0 dB, respectively, for the SCS of 240 (120) kHz. We conclude that the multiplexing scheme for the PSS and SSS and their sequences are effective in achieving a high PCID detection probability considering the large frequency offset even with ε = 30 ppm in the 28-GHz band.

This paper presents the bit error rate (BER) performance of frequency domain equalization (FDE) using cyclic-shifted code division multiplexing (CDM) pilot signals for single-carrier line-of- sight (LOS) - multiple-input multiple-output (MIMO) multiplexing. We use different cyclic-shift resources of the same Zadoff-Chu sequence for transmission-stream-specific pilot signals that are essential for estimating the channel response for FDE and phase noise in LOS-MIMO. Computer simulation results show that the required received signal-to-noise power ratio satisfying the BER of 10-4by averaging approximately 4 channel responses after despreading the pilot signal in the frequency domain is decreased by approximately 2.0 dB compared to that without averaging of the channel response for 256QAM, 1024QAM, and 4096QAM in 2×2 and 4×4 LOS-MIMO. Through the simulation results, we show that CDM-based pilot signal multiplexing with different cyclic shifts and the frequency domain averaging of the estimated channel response are effective in achieving accurate channel estimation with a short delay and a low pilot-overhead loss for single-carrier LOS- MIMO.

This paper presents the physical-layer cell identity (PCID) detection probability considering frequency offset for 5th generation (5G) new radio (NR). We compare the primary synchronization signal (PSS) and PCID detection probabilities of three PSS detection methods: cross-correlation based detection before frequency offset (FO) estimation and compensation, that after FO estimation and compensation, and autocorrelation based detection at a set of user equipment. Link- level simulation results show that the cross- correlation based PSS detection before the FO estimation and compensation achieves the highest PSS and PCID detection probabilities in the carrier frequency fc region lower than approximately 14 GHz at the average received signal-to-noise power ratio of 0 dB for the standard oscillator frequency error of 1 ppm. The cross-correlation based PSS detection after the FO estimation and compensation achieves much higher PSS and PCID detection probabilities than that before the FO estimation and compensation for the fc region higher than approximately 14 GHz. The PCID detection probability of the cross-correlation based PSS detection after the FO estimation and compensation is close to that of the autocorrelation based PSS detection according to the increase in the fc value. Therefore, we conclude that by switching the cross- correlation based PSS detection methods before and after the FO estimation and compensation, the PSS and secondary synchronization signal structures based on the NR radio interface achieve a high PCID detection probability for the fc value up to 60 GHz.

The authors analyse and investigate the effectiveness of frequency domain equalisation (FDE) for single‐carrier (SC) transmission over a line‐of‐sight multiple‐input multiple‐output (LOS‐MIMO) channel with frequency selective fading. For this purpose, they propose a LOS‐MIMO system model employing SC‐FDE techniques together with a data frame structure having a cyclic prefix and postfix (CPP) overhead. The channel capacity of the proposed system is derived taking into account system design parameters, such as symbol rate and roll‐off factor, as well as multipath fading channel parameters. An efficient channel estimation method is also proposed for implementing and simulating the proposed system. Signature curves estimated in simulations are consistent with those expected from the theoretical capacity analysis. The simulation results show that the SC‐FDE approach to the LOS‐MIMO system can, with small CPP overhead, effectively reduce intersymbol and interstream interference.

This paper proposes a time-synchronized control-channel multiplexing scheme using cyclic-shifted Zadoff-Chu sequences for full duplex (FD) aiming at decreasing the latency due to feedback control signals. In the proposed scheme, a set of different cyclic-shift resources of a Zadoff-Chu sequence with the same root index are assigned to control signals in both the downlink and uplink that are multiplexed in time-synchronized subframes accompanied with a cyclic prefix and cyclic suffix. Because the cross-correlation of the different cyclic-shifted Zadoff-Chu sequences with the same root index is quite low, the self-interference (SI) or co-channel interference (CCI) that leaks from its own transmitter or that of another set of user equipment to a receiver is suppressed to a very low level after despreading in the frequency domain. As a result, the significantly reduced SI or CCI after despreading results in a decreased level of complexity for the SI or CCI canceller, i.e., particularly the digital interference canceller. The computed cross-correlation results show that the cross-correlations among different cyclic-shift indices become almost zero. Based on the computed cross-correlations of the cyclic-shifted Zadoff-Chu sequences, we discuss the receiver structures including SI rejection methods for a base station and UE. Because control signals are multiplexed in every subframe in the downlink and uplink, the proposed control-channel multiplexing is applicable to low-rate control signals that require low latency.

This paper proposes frequency diversity (FD) reception for narrowband (NB) primary synchronization signal (NPSS) and narrowband secondary synchronization signal (NSSS) in order to improve the physical-layer cell identity (PCID) detection probability for NB-Internet-of-Things (IoT) communications. In the proposed FD reception, a user equipment receives the NPSS and NSSS in a radio frame alternately in time domain by switching the received NPSS and NSSS each those are transmitted from different resource blocks in the same frequency band. Link-level simulation results show that the PCID detection probability using FD reception is improved by approximately 16% compared to that without FD reception using the FD separation of four resource blocks with single antenna transmission. These results suggest that the average time for computing the cost functions of the NPSS is decreased to approximately 1/3 that without FD reception for detecting the NPSS received timing. We also show that the PCID detection probabilities of 90% and 97% are achieved using FD reception with precoding vector switching (PVS) transmit diversity at the average received signal-to-noise power ratio of 0 dB for the case with the maximum frequency offset of 70 kHz and that without considering frequency offset, respectively.

In full duplex (FD), which improves frequency efficiency and achieves flexible resource assignment between the uplink and downlink, the throughput cannot be improved to an ideal level due to self-interference (SI) from a transmitter, asymmetric traffic loads in the downlink and uplink, and other-cell interference. This paper proposes physical channel multiplexing using symbol repetition in every subframe for FD to improve the achievable throughput with an asymmetric traffic distribution. In the proposed physical channel multiplexing scheme, by employing symbol repetition in every subframe in the link with a low traffic load, i.e., the uplink typically, decreasing the power resource per symbol brings about an increase in throughput in the link with a high traffic load, i.e., the downlink, by decreasing the SI power level for FD. We describe the effect of latency and the implementation of an SI canceller focusing on a digital self-interference canceller (DSIC) for the proposed physical channel multiplexing scheme. We also show that the signal-to-interference plus noise power ratio (SINR) at the demodulator input is increased by employing the symbol repetition in every subframe, which leads to an increase in throughput in the link with a high traffic load for FD.

Recently, we proposed a high-order circular quadrature amplitude modulation (QAM) constellation scheme with a high low-density parity-check (LDPC) coding rate that is suitable for partial LDPC coding associated with parallel double Gray mapping for microwave mobile backhaul. This paper presents the bit error rate (BER) performance of circular QAM when using a combination of Wiener filter based pilot symbol assisted (PSA) and phase locked loop (PLL) phase noise (PN) estimation and compensation methods. Computer simulation results show that the required received signal-to-noise power ratio (SNR) at the BER of 10-6using the PSA and PLL PN estimation and compensation is decreased by approximately 0.3, 0.6, and 1.3 dB for the pilot symbol insertion interval of 25, 50, and 100 symbols, respectively, compared to that using only the PSA PN estimation for circular 1024QAM. Accordingly, we show that the PLL PN estimation is effective in decreasing the pilot symbol overhead of PSA PN estimation for circular QAM, which is robust against time-varying PN.

This paper proposes a fast cell search method using maximum likelihood detection (MLD) based frequency offset estimation for a small cell in Long Term Evolution (LTE) heterogeneous networks (HetNets). In the proposed cell search method, a set of user equipment (UE) estimates the primary synchronization signal (PSS) timing and frequency offset using different PSS correlation computation methods in a macrocell or a small cell according to the employed carrier frequency. For a macrocell, we use the conventional cross- correlation based detection. Meanwhile, for a small cell with a high carrier frequency, a UE first detects the maximum autocorrelation peak between the received sample signals that are five milliseconds apart. Then, the UE estimates the fractional frequency offset from the phase rotation between two consecutive PSSs. After compensating for the fractional frequency offset, the UE simultaneously detects the accurate frequency offset that provides the phase rotation of 2PIxG (G denotes an integer) over the multiplexed interval of two PSSs and the PSS sequence based on MLD. After selecting the best cell, the UE detects the best secondary synchronization signal (SSS) sequence by taking the SSS sequence correlation for the received signal. System-level simulation results show that the proposed cell search method achieves a fast initial cell search time within approximately 120 ms to satisfy the physical cell ID detection probability of 95% even for the carrier frequency of a small cell up to 12 GHz, assuming the free- running frequency error of the UE standard oscillator of 3 ppm.

This paper proposes a fast initial cell search method based on two-step frequency offset estimation for a small cell in Long Term Evolution (LTE) heterogeneous networks using different frequency spectra. In the proposed cell search method, a set of user equipment (UE) first estimates the frequency offset of a received primary synchronization signal (PSS) from a macrocell and computes the frequency offset of a received PSS for a small cell in Step 1 assuming the same frequency error of a temperature compensated crystal oscillator (TCXO) of a UE. The UE detects the PSS received timing from the maximum PSS correlation after compensating for the frequency offset by using the estimated value in Step 1 for the small cell. In Step 2, the UE estimates the residual frequency offset by taking a partial correlation of the PSS from the small cell. The UE detects the best secondary synchronization signal (SSS) sequence by taking the SSS sequence correlation for the received signal after compensating for the frequency offset using the estimated value in Step 2. System- level simulation results show that the proposed cell search method achieves a fast initial cell search time within approximately 150 ms to satisfy the cell ID detection probability of 95% even for the carrier frequency of a small cell up to 6 and 11 GHz, assuming the free-running frequency error of the UE TCXO of 3 and 1 ppm, respectively.

This paper presents the initial cell search time performance based on Long Term Evolution (LTE) synchronization signals employing precoding vector switching (PVS) transmit diversity in heterogeneous networks. We focus on the effect of PVS transmit diversity to mitigate the influence of co-channel interference in heterogeneous networks with the same frequency spectrum between a macrocell and small cells. System-level simulation results show that when using two-antenna receive diversity, the cell search time at the cell ID detection probability of 98% using PVS transmit diversity is decreased by approximately 20 ms than for one-antenna transmission. Moreover, we show that the PVS transmit diversity is more effective for inter-macrocell synchronous operation compared to that for inter-macrocell asynchronous operation. Through the simulation results, we show that PVS transmit diversity is beneficial in achieving fast initial cell search times in heterogeneous networks with the same frequency spectrum.

This paper investigates the block error rate (BLER) performance of time and frequency domain compression for Faster-than-Nyquist (FTN) signaling in frequency-selective fading channels. In this paper, we use FTN mapping method in which FTN symbols are mapped onto orthogonal frequency division multiplexing (OFDM)/offset quadrature amplitude modulation (OQAM) symbol positions at a transmitter and a turbo soft interference canceller (SIC) used for an antenna-diversity receiver. Computer simulation results show that frequency domain compression decreases the required average received signal-to-noise power ratio satisfying the target average BLER compared to time domain compression when the root mean square (r.m.s.) delay spread is longer than approximately 1.5 μs. We also show, however, that the FTN signaling with time domain compression achieves a higher frequency efficiency compared to that with frequency domain compression when the r.m.s. delay spread is less than 1.5 μs.

This paper presents the initial cell search time performance based on Long Term Evolution (LTE) synchronization signals employing the same frequency spectrum for heterogeneous networks including indoor small cells. We assume the indoor small cell models in hot zone buildings that are specified in the 3rd Generation Partnership Project (3GPP) technical report. System-level simulation results show that in both the sparse and dense scenarios employing the same frequency spectrum for the heterogeneous networks, the influence of co-channel interference particularly from a macro cell to indoor small cells on the initial cell search time is not large except for the case when a small cell cluster is placed very close to the macro cell site. We also show that the indoor small cell deployment is effective in achieving fast cell search times as well as achieving higher cell throughput for heterogeneous networks where high volume traffic occurs in the indoor hot zone building.

This paper proposes a fast initial cell search method based on frequency offset estimation for Long Term Evolution (LTE) heterogeneous networks using separate frequency spectra between a macrocell and a small cell. When using the primary synchronization signal (PSS) and secondary synchronization signal (SSS) in the LTE radio interface, the initial cell search time for small cells with a high carrier frequency becomes very long due to the false detection of the PSS received timing due to the large frequency offset. In the proposed initial cell search method, we first measure the frequency error of a temperature compensated crystal oscillator (TCXO) of a set of user equipment for a macrocell with the carrier frequency of 2 GHz. Based on the estimated frequency offset, we detect the correct PSS received timing among the probable timing candidates for a small cell that are estimated from the correlation between the received signal with the 3.5-GHz carrier frequency and PSS sequence replica for small cells. System-level simulation results show that by using the proposed cell search method, the cell search time to achieve the cell ID detection probability of 99% is within approximately 100 ms even with the large frequency offset of 10.5 kHz.

This paper investigates the throughput performance using adaptive modulation and coding (AMC) focusing on the causes of impairment to Orthogonal Frequency Division Multiplexing (OFDM) - Multiple-Input Multiple-Output (MIMO) multiplexing. We first investigate the influence of a limited number of modulation and coding schemes (MCSs) and channel estimation error for MCS selection based on mutual information (MI). Second, we clarify the effect of MCS selection error on an increasing maximum Doppler frequency due to the round trip delay time (RTT) in comparison to the throughput upper bound that is computed from the MCS combination providing the maximum throughput considering the block error. Third, we clarify the effect of channel estimation error of maximum likelihood detection (MLD) when using reference signal (RS) based channel estimation in comparison to ideal channel estimation. Through the evaluations, we clarify the impairment factors that degrade the achievable throughput for OFDM-MIMO multiplexing using AMC in an actual multipath fading channel.

This paper presents a comparative study of single-carrier (SC)-frequency division multiple access (FDMA) and OFDMA using turbo soft interference cancellation (SIC) from the viewpoint of throughput for multiple-input multiple-output (MIMO) spatial division multiplexing (SDM). In turbo SIC, interference from other transmission streams is generated based on the log-likelihood ratio (LLR) at the turbo decoder output and subtracted from the received signal iteratively associated with a linear minimum mean-square error (LMMSE) filter. Hence, we compare the throughput performance levels of methods for generating soft-symbol estimates of other streams based on the extrinsic LLR and the a posteriori LLR at the Max-Log-MAP decoder output. We show by computer simulation the difference in performance of turbo SIC based on the a posteriori LLR and extrinsic LLR from the viewpoints of the average block error rate and throughput. We also show that the OFDMA yields superior throughput performance compared to SC-FDMA with 16QAM and 64QAM schemes when using turbo SIC for 2-by-2 to 8-by-8 MIMO SDM.

This paper proposes local cell cluster-specific primary synchronization signal (PSS) sequence assignment and local cell-specific secondary synchronization signal (SSS) sequence assignment schemes for orthogonal frequency division multiple access (OFDMA) heterogeneous networks. The proposed synchronization signal (SS) sequences are based on those of the Long-Term Evolution (LTE) radio interface. We investigate the effects of the proposed SS sequence assignments from the viewpoint of the initial cell search time for various inter-cell site synchronization modes based on system-level simulations. We show that the local cell cluster-specific PSS sequence assignment achieves fast cell search time performance that is almost the identical level to that assuming the cell arrangement with a macrocell only. We show, however, that the effect of the new local cell-specific SSS sequences based on cyclic-shifted M-sequence in addition to the current 168 SSS sequences is small from the viewpoint of reducing the initial cell search time.

This paper proposes channel state information - reference signal (CSI-RS) multiplexing employing carrier frequency swapping for frequency division duplex (FDD) high-order multiple-input multiple-output (MIMO) spatial division multiplexing (SDM). In the proposed CSI-RS multiplexing method, the carrier frequency of a fast Fourier transform (FFT) block for multiplexing time division duplex (TDD) CSI-RSs within a subframe is swapped between the downlink and uplink. By using the proposed TDD CSI-RS multiplexing method, the CSI for performing precoding and link adaptation is estimated in the reverse link by taking advantage of the channel reciprocity feature. By using the proposed TDD CSI-RS multiplexing method, the RS overhead is decreased according to the increase in the number of simultaneously accessing sets of user equipment for multiuser MIMO. Moreover, the proposed TDD CSI-RS multiplexing method does not need fast feedback signals that track instantaneous channel response including the channel quality indicator (CQI), rank indicator (RI), and precoding matrix indicator (PMI) except for the slow feedback of the average interference level from the surrounding cells.

This paper presents the block error rate (BLER) performance of a posteriori log-likelihood ratio (LLR) computation methods at the output of a frequency domain equalizer (FDE) with antenna diversity reception using a low-rate turbo code for discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). In the paper, we propose an a posteriori LLR computation method based on the minimum squared Euclidean distance of the signal after coherently combining the FDE output of all receiver diversity branches. We compare the BLER performance level of the proposed LLR computation method to that for the conventional LLR computation method in which the a posteriori LLR is given as a summation of the minimum squared Euclidean distances of all receiver branches. In the BLER comparison, we consider the influences of noise correlation after frequency domain equalization and the channel estimation error. Computer simulation results show that the LLR computation using the signal after combining the receiver branches is more appropriate than the LLR computation with combining the squared minimum Euclidean distances in the probability domain with a low-to-high turbo coding rate as the a posteriori LLR at the FDE output associated with receiver diversity for DFT-precoded OFDMA.

This paper presents the performance of outer-loop control for adaptive modulation and coding (AMC) using mutual information (MI) based mapping between the block error rate (BLER) and received signal-to-interference plus noise power ratio (SINR) in the multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) downlink employing maximum likelihood detection (MLD). In AMC, we generate a mapping table between the BLER and MI per bit in advance, which is computed from the received SINR, assuming typical channel conditions including the path model and fading maximum Doppler frequency. Then, in the proposed outer-loop control, the measured MI per bit value for selecting the best modulation and coding scheme (MCS) is adjusted so that the measured BLER after turbo decoding satisfies the prescribed target value. Computer simulation results show that the outer-loop control achieves almost the same throughput as that with a mapping table assuming channel conditions identical to those for the actual measurement, while achieving nearly the identical target BLER. Moreover, we show that the best step size, which provides nearly the maximum throughput, differs according to the change in the maximum Doppler frequency in contrast to the relative feedback delay of the AMC loop. Nevertheless, it is insensitive to the target BLER value and frequency-selectivity of a channel model.

A low-rate turbo code can reduce the required average received signal-to-noise power ratio (SNR) that satisfies the target block error rate (BLER) due to its high coding gain. When a low-rate turbo code is used however, channel estimation (CE) error becomes a bottleneck in bringing out the potential coding gain. Therefore, this paper presents the average BLER performance using decision-directed channel estimation (DDCE) for a low-rate turbo code in uplink Discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). In the proposed DDCE, we employ soft-decision symbol estimation based on the log-likelihood ratio (LLR) of an extrinsic probability at the Max-Log-MAP (maximum a posteriori probability) decoder output in addition to reference signals (RSs). The DDCE works synergistically with the low-rate turbo code, since the extrinsic LLR at the Max-Log-MAP decoder becomes more reliable due to the increasing coding gain. Computer simulation results show that when the turbo code with R = 1/15 (1/9) and the constraint length of K = 4 bits is used, the required average received SNR at the average BLER of 10-2using the DDCE is decreased by approximately 0.6 (0.4) dB compared to that for the RS based CE. As a result, the required average received SNR using the DDCE for R = 1/15 and 1/9 is decreased by approximately 7.0 and 5.0 dB, respectively, compared to that for R = 1/3.

This paper proposes a combination of open-loop (OL) transmit diversity and intra-subframe frequency hopping (FH) for a shared channel carrying user traffic data and investigates the potential performance of the combination compared to closed-loop (CL) transmit diversity for uplink discrete Fourier transform (DFT)-precoded OFDMA in frequency-selective fading channels. We apply FH to OL transmit diversity to mitigate the reduction in the diversity gain under high fading correlation conditions among antennas and decision-feedback channel estimation (DFCE) to improve the channel estimation accuracy. Computer simulation results show that the loss in the required average received signal-to-noise power ratio (SNR) at the average block error rate (BLER) of 10-2 of space-time block code (STBC), i.e., OL transmit diversity, with intra-subframe FH compared to codebook-based CL transmit diversity is reduced to within approximately 0.8 dB using DFCE at maximum Doppler frequency of fD = 5.55 Hz. Moreover, it is shown that STBC with FH and DFCE achieves much better BLER performance than CL transmit diversity when fD is higher than approximately 80 Hz due to the degradation in the tracking ability against fast fading variation in the feedback loop of CL transmit diversity.

This paper proposes applying intra-subframe frequency hopping (FH) to closed-loop (CL) type transmit diversity using codebook based precoding for a shared channel carrying user traffic data in the uplink discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the paper, we present two types of precoding schemes associated with intra-subframe FH: individual precoding vector selection between 2 slots where a 1-msec subframe comprises 2 slots among the reduced precoding codebooks, and common precoding vector selection between 2 slots. We investigate the effect of intra-subframe FH on the CL type transmit diversity with precoding in terms of the block error rate (BLER) performance while maintaining the same number of feedback bits required for notification of the selected precoding vector as that for CL type precoding based transmit diversity without FH. Computer simulation results show that CL type transmit diversity with precoding using intra-subframe FH is very effective in reducing the required average received signal-to-noise power ratio (SNR) when the fading maximum Doppler frequency, fD, is higher than approximately 50 Hz both for 2- and 4-antenna transmission in the uplink DFT-precoded OFDMA.

This paper proposes an inter-code interference canceller (ICIC) for control signals carried by the Physical Uplink Control Channel (PUCCH) in the Long-Term Evolution (LTE) uplink using Discrete Fourier Transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the proposed ICIC, a soft interference replica of another cyclic-shifted code channel for data symbols is generated from the log-likelihood ratio (LLR) of a posteriori probability (APP) in Max-Log-MAP and a complex fading envelope estimated using reference signals (RSs), and subtracted from the received signal iteratively. We also propose RS multiplexing employing a combination of block spread (BS) and cyclic shift (CS) for two RS symbols within a slot to achieve accurate channel estimation. Computer simulation results show that the proposed ICIC associated with RS multiplexing using a combination of BS and CS is effective in reducing the required average received signal-to-noise power ratio (SNR) even for 12 PUCCH multiplexing in frequency-selective fading channel with long delay spread.

This paper presents cell search time performance using multipath signals in the Long-Term Evolution (LTE) downlink employing Orthogonal Frequency Division Multiple Access (OFDMA) in inter-cell site asynchronous operation. In the paper, we propose primary synchronization signal (PSS) detection using multipath signals based on window detection and secondary synchronization signal (SSS) detection using coherent summation of channel estimates weighted by the frequency domain channel response of typically assumed multipath signals. Computer simulation results show that the effect of using multipath signals for PSS detection on the overall cell search time performance is slight, and the maximum correlation peak detection for the PSS provides a sufficiently fast cell search time. The results also show that coherent averaging of channel estimates using the PSS to detect the eNode-B-specific SSS sequence is effective in achieving a fast cell search time, and the achievable cell search time is insensitive to the weighting factor as long as the interval of the coherent summation is optimized for the respective power delay profiles.

In this paper, in order to achieve the available spatial, temporal and frequency diversities, and also make the system implementation feasible for high speed orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing, a novel LSTF transmitter architecture with multiple channel encoders is proposed with each independently coded information sub-stream being threaded in the three-dimensional (3-D) space-time-frequency transmission resource array. The performance of a receiver consisting of a maximum-likelihood detector with QR decomposition and M-algorithm (QRM-MLD) is exploited, by employing irregular low-density parity-check (LDPC) code as the channel code. The threaded distribution of each coded information sub-stream in the proposed LSTF makes it to achieve the spatial, temporal and frequency diversities the same as the conventional single-encoder LSTF where coding is applied across the whole information stream, and simulation results show that the performance of the proposed multiple-encoder LSTF architecture is very close to that of the conventional single-encoder LSTF. However, due to the use of multiple parallel encoders/decoders with a shorter codeword length, the proposed LSTF architecture has much lower hardware processing speed and complexity than the conventional LSTF.

The long-term evolution (LTE), which was specified as the release 8 specification in the 3rdgeneration partnership project (3GPP), will achieve broadband services with the peak data rate of 100 Mbps in the downlink. This paper presents the measured throughput performance and power consumption performance of the implemented demodulation and decoding LSI for 2-by-2 MIMO-OFDM in the Rel-8 LTE downlink. The implemented LSI comprises FFT timing detection, a 2048-point FFT, a channel estimation filter, maximum likelihood detection (MLD) based signal detection, a channel deinterleaver, and a turbo decoder with the max-log-MAP (maximum a posteriori) algorithm. The most prominent feature of the implemented LSI is MLD based signal detection with low power consumption and a low required received signal-to-noise power ratio (SNR) for 2-by-2 MIMO multiplexing. Experiments show that the implemented LSI achieves the measured throughput of 100 Mbps at the average received SNR of 22 dB with a low power consumption level of approximately 40 mW with 16QAM and the channel coding rate of 8/9.

This paper proposes the optimum radio link connection (RLC) using remote radio equipment (RRE) in a heterogeneous network in which various types of cell configurations exist with different cell sizes and downlink transmission power levels for LTE (Long-Term Evolution)-Advanced. The instantaneous received signal-to-interference plus noise power ratio (SINR) and the user throughput performance employing the proposed RLC methods are investigated using system-level simulations. From the simulation results, we show that the proposed independent RLC method between the downlink and uplink and the proposed multipoint RLC method based on coordinated multipoint transmission/reception achieve a higher user throughput both in the downlink and uplink compared to the conventional common RLC method. Therefore, the proposed independent and multipoint RLC methods are very promising candidates to improve the user throughput particularly near the cell edge in a heterogeneous network for LTE-Advanced.

This paper presents a comparison based on the block error rate (BLER) performance of cyclic shift (CS) and block spreading (BS) CDMA using codeword maximum likelihood detection (MLD) and joint MLD that take advantage of the channel coding information for the Physical Uplink Control Channel (PUCCH) in the Evolved UTRA uplink. We first present the BLER performance of CSand that for BS-CDMA using codeword MLD and joint MLD in the GSM Typical Urban, ITU-R Vehicular-A, and Pedestrian-B channel models. Then, we compare the BLER performance between CS-and BS-CDMA in an exponentially decayed power delay profile model to focus on large delay spread environments in a macrocell. Simulation results show that although BS-CDMA is superior to CS-CDMA due to a lower required received signal-to-noise power ratio (SNR) in small delay spread environments, CS-CDMA using joint MLD is more appropriate than BS-CDMA to support small-to-large delay spread environments in a unified manner.

This paper investigates the optimum radio parameters, i.e., numerology, in layered orthogonal frequency division multiple access (OFDMA) for long-term evolution (LTE)- Advanced. Similar to the layered OFDMA concept, it was agreed at the 3GPP RAN WG1 meeting that the entire transmission bandwidth in LTE-advanced should comprise multiple frequency blocks called component carriers to achieve a wider system bandwidth than that for the current LTE (Rel-8 LTE). We investigate the optimum radio parameters in the frequency domain including the need for an inter-component carrier guard band (GB). In the simulation evaluations, we set the parameters for the receiver filter assuming the worst case that satisfies the minimum requirement specified in Rel-8 LTE. Simulation results show that the loss in the average received signal energy per symbol-to-noise power spectrum density ratio (Es/No) satisfying the required block error rate compared to the case without an inter-component carrier GB is negligible irrespective of the modulation scheme and coding rate. As a result, we conclude that the inter-component carrier GB is unnecessary and can be minimized to 19 subcarriers in the downlink while retaining the same number of subcarriers within a component carrier as that for Rel-8 LTE.

This paper experimentally investigates the effect of frequency error compensation via demodulation automatic frequency control (AFC) using the Synchronization Channel (SCH) in downlink OFDM radio access. The implemented OFDM receiver compensates for the frequency error caused by the difference in frequency between a base station (BS) and a user equipment (UE) using a time-division multiplexed SCH signal and that caused by the Doppler shift generated by the mobility of a user using reference signals with staggered multiplexing. Experimental results elucidate that even when the standard oscillator frequency of UE cannot track the more accurate one of a BS, demodulation AFC can suppress the residual frequency error to a sufficiently low level using the SCH so that the degradation in the block error rate of the physical broadcast channel control signals is slight with respect to the case without frequency error for a speed greater than 350 km/h.

Single carrier (SC)-FDMA has been adopted by 3GPP as the radio access scheme for the uplink of long term evolution (LTE). The uplink Layer 1 / Layer 2 (L1/L2) control signalling information consists of ACK/NACK and channel quality indicator (CQI) etc. Frequency hopping based uplink L1/L2 control channel structures for ACK/NACK and CQI are agreed. This paper proposes user equipment (UE, i.e., handset or mobile terminal) specific cyclic shift (CS) setting based on the agreed hopping structure in order to achieve further interference averaging effect and diversity effect. The simulation results show that proposed UE-specific CS hopping can provide additional intra and inter-subframe interference randomization effect and hence additional gain compared to the case without further CS hopping.

Tins paper presents the most appropriate transmit diversity scheme for the synchronization channel (SCH) employing the latest radio interface for the SCH structure and sequences based on system-level simulations in the evolved UTRA downlink. The transmit diversity candidates assumed in the paper are preceding vector switching (PVS), time switched transmit diversity (TSTD), cyclic delay diversity (CDD), and frequency switched transmit diversity (FSTD) based on the features of the SCH. Simulation results show that transmit diversity is effective in increasing detection probabilities of SCH timing detection in the first step and the cell ID group-specific SCH sequence in the second step of the cell search process. Moreover, we clarify that PVS is the best transmit diversity scheme for the SCH based on the reduction in the cell search time. We show that PVS achieves fast cell search in less than approximately 20 msec at the location probability of 90% regardless of the inter-site distance up to 10 km.

This paper proposes layered orthogonal frequency division multiple access (OFDMA) radio access for LTE (long-term evolution)-advanced to achieve higher-level system requirements than those in Release 8 LTE called Evolved UMTS terrestrial radio access (UTRA) and UMTS terrestrial radio access network (UTRAN). Layered OFDMA comprises layered transmission bandwidth assignment according to the required data rate, a layered control signaling structure, and support for layered environments in which an adaptive multi-access scheme with hybrid single-carrier and multicarrier based radio access is applied. layered OFDMA radio access will support all functionalities provided in Release 8 LTE and its enhancement. Key radio access techniques such as fast inter-cell radio resource management that take advantage of remote radio equipment (RRE) aiming at inter-cell orthogonality, multi-antenna transmissions with more antennas, and coverage enhancing techniques are used to achieve a high level of capacity and cell-edge spectrum efficiency.

This paper presents indoor and field experimental results on extremely high-speed packet transmissions of 4.92 Gbps in a 100 -MHz channel bandwidth, i.e., the frequency efficiency of approximately 50 bit/second/Hz, in the downlink OFDM radio access. The required received signal-to-noise power ratio (SNR) is less than 30dB, which is almost the upper limit in cellular environments near a cell site even with a light channel load, with the aim of application to future universal broadband packet radio access. We apply 12-by-12 MIMO multiplexing using the maximum likelihood detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of the surviving symbol replica candidates (ASESS),64QAM data modulation, and Turbo coding with the coding rate of R = 8/9 to achieve an extremely high frequency efficiency level. In the field experiments conducted in the Yokosuka Research Park (YRP) district of Yokosuka city, we show that the measured throughput of 4.92 Gbps is achieved at the average received SNR per receiver antenna of approximately 28.0 and 28.5 dB when the respective receiver antenna separation is 40 cm (6.2lambda) and 10 cm (1.5lambda) and the transmitter antenna separation is 70 cm (10.9lambda) at the average speed of 10 km/h under non-line-of-sight (NLOS) conditions.

This letter investigates the effect of Doppler frequency shift on the performance of MMSE receivers for high speed variable spreading factor (VSF) orthogonal frequency and code division multiplexing (OFCDM) systems in broadband wireless communications. In VSF-OFCDM systems, the existence of multicode interference (MCI) resulting from multiple code channels occupying the same bandwidth degrades the performance. A full MMSE receiver is analytically studied in this letter, exploiting correlation properties among transmitted data on different subcarriers to combat the MCI. Furthermore, considering the fact that the fast time-varying fading destroys the orthogonality of the time domain spreading codes and thus introduces time domain MCI, its effect on system performance is evaluated accurately. It is also shown that it is expected to use time domain spreading factor NTof 8 for a large range of Doppler frequencies, and frequency domain spreading factor as large as possible, especially in high signal to noise ratio. Moreover, in order to improve performance, the pilot channel should occupy around 20% to 25% of the total transmitted power for a large range of Doppler.

This paper proposes the application of closed-loop type antenna switching transmit diversity (ASTD) associated with frequency domain channel-dependent scheduling to single-carrier frequency division multiple access radio access in the evolved UTRA (UMTS terrestrial radio access) uplink. In the proposed scheme, virtual resource units (RUs) are assigned to the optimum transmitter antenna in the spatial domain, while they are also assigned to the optimum frequency band (i.e., physical RUs) in the frequency domain according to the propagation channel conditions of each user. The reference signal overhead is the same as that for single-antenna transmission and the impact on the hardware implementation in the user equipment is slight since only one RF chain is necessary. Simulation results show that the gain of the closed-loop type ASTD is approximately 1.2-1.5 dB at the 1% level in the cumulative distribution function, assuming unequal antenna gain, i.e., the difference in the average transmission power of 3 dB and the fading correlation between transmitter antennas of 0.3 when frequency domain channel-dependent scheduling is applied with hybrid ARQ and soft-combining.

This paper presents the optimum channel coding and multiplexing schemes for Layer 1 (Ll)/Layer 2 (L2) control signals for OFDM based radio access in the Evolved UTRA downlink. Simulation results show that separate channel coding of downlink-related L1/L2 control signals is superior to joint coding among simultaneous accessing user equipments (UEs), from the viewpoint of the required total symbol energy of the L1/L2 control signals. The results also show that time division multiplexing (TDM) based multiplexing associated with transmission time interval (TTI)-by-TTI frame format control employing a control channel format indicator (CCFI) achieves almost the same cell throughput as that for frequency division multiplexing (FDM). Therefore, considering the advantages of TDM such as the possibility of a power saving effect through micro-sleep operation and a short control loop delays for scheduling, adaptive modulation and coding, and hybrid ARQ, we conclude that TDM based multiplexing of L1/L2 control signals with a shared data channel is superior to using FDM based multiplexing.

This paper proposes a handover method that uses a combination of bicast and forwarding (BIFO) of IP packets to achieve a short handover delay time and a low amount of IP packet traffic in the backhaul for future IP-based radio access networks (RANs). To validate the effect of the proposed BIFO method, we implemented prototype experimental equipment comprising a RAN_access router (RAN_AR), base stations (BSs) associated with a radio control server (RCS), and user equipment (UE) including a controller. The experimental results show that the BIFO achieves a shorter handover delay time than when using only the conventional bicast method or forwarding method by taking advantage of the respective merits of bicast and forwarding. The results also confirm that the BIFO method achieves the handover delay time in the control plane of approximately 10 - 20 msec.

Single-Carrier (SC)-FDMA based radio access in the evolved UTRA uplink that is necessary for downlink scheduling, link adaptation, hybrid ARQ (automatic repeat request) with soft-combining, and for uplink feedback control signaling. We propose SC-based multiplexing of L1/L2 control signaling with a shared data channel for a set of user equipment (UE) that transmits both an uplink shared data channel and L1/L2 control channel within the same sub-frame. We also propose an L1/L2 control signaling multiplexing scheme without uplink data transmission that takes advantage of frequency hopping using multiple exclusively-assigned time-frequency resources to achieve the frequency diversity effect. Computer simulation results show that the proposed SC-based multiplexing of the L1/L2 control channel with the shared data channel achieves a higher user throughput than multicarrier-based multiplexing. The results also show that the proposed L1/L2 control signaling multiplexing scheme for the UE without uplink data transmission achieves both high quality reception through large frequency diversity and an increase in coverage through full use of the transmission time duration compared to the conventional schemes.

This paper presents the optimum primary- synchronization channel (P-SCH) and secondary-SCH (S-SCH) sequences for the SCH based on criteria to achieve fast initial and neighboring cell search time performance in the Evolved UTRA (E-UTRA) downlink. Simulation results show that the P-SCH sequence has a slight influence on the achievable cell search time, and that the application of multiple sequences, i.e., three P-SCH sequences, is beneficial in achieving fast cell search time performance particularly for the neighboring cell search. The results also show that the Walsh-Hadamard sequence or cyclic-shifted orthogonal sequence is suitable for the S-SCH sequence to indicate the cell ID group. Furthermore, it is shown that the combination of a permutation of the orthogonal S-SCH and P-SCH-specific scrambling sequences is advantageous in suppressing the cross-correlation between S-SCHs that collide and in achieving a fast cell search time particularly for the neighboring cell search in inter-node B synchronous operation.

This paper presents a performance comparison of the initial cell search time and neighboring cell search time using hierarchical and non-hierarchical synchronization channel (SCH) structures in order to establish the optimum SCH structure in the evolved UTRA downlink. Computer simulation results show that in a 19-cell configuration, the cell search time at the 90% cumulative distribution function using the hierarchical SCH structure is less than half that using the non-hierarchical SCH structure in a neighboring cell search under low signal-to-interference plus noise power ratio conditions, although both structures achieve almost the same cell search time in the initial cell search. This is due to the cross-correlation based SCH symbol timing detection in the hierarchical SCH structure, which is affected less by noise than auto-correlation based detection in the non-hierarchical SCH structure. Thus, we conclude that the hierarchical SCH structure is more appropriate than the non-hierarchical SCH structure based on the cell search time performance especially in the neighboring cell search.

This paper proposes a group-wised reference signal (RS) for channel quality indicator measurement in frequency domain channel-dependent scheduling employing adaptive control of the transmission bandwidth in the single-carrier frequency division multiple access-based evolved UMTS terrestrial radio access uplink. In the proposed method, fluctuation in the interference power imparted to the surrounding cells is suppressed to a low level, and both the user throughput for a user equipment (UE) near the cell edge and the cell throughput are improved compared to the conventional uniform RS allocation due to reductions in the error when selecting the optimum UE in channel-dependent scheduling and selecting the modulation and coding scheme in the adaptive modulation and channel coding. Simulation results show that the user throughput at the 5% cumulative distribution function value when employing the proposed group-wised sounding RS allocation with the adaptive transmission bandwidth is increased by approximately 75% and 65% for the inter-site distance of 500 and 1732 m, respectively, compared to that using a uniform RS allocation, while achieving almost the same level of cell throughput.

This paper presents indoor and field experimental results on extremely high-speed packet transmissions of 4.92 Gbps in a 100-MHz channel bandwidth, i.e., the frequency efficiency of approximately 50 bit/second/Hz, in the downlink orthogonal frequency division multiplexing (OFDM) radio access. The required received signal-to-noise power ratio (SNR) is less than 30 dB, which approaches the almost upper limit in cellular environments near a cell site even with a light channel load, with the aim of the application to future universal broadband packet radio access. We apply 12-by-12 MIMO multiplexing using the maximum likelihood detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of the surviving symbol replica candidates (ASESS), 64QAM data modulation, and turbo coding with the coding rate of R = 8/9 to achieve an extremely high frequency efficiency level. In the field experiments conducted in the Yokosuka Research Park (YRP) district of Yokosuka city, we show that the measured throughput of 4.92 Gbps is achieved at the average received SNR per receiver antenna of approximately 28.0 and 28.5 dB when the receiver antenna spacing is 40 cm (6.2lambda), and 10 cm (1.5lambda) at the average speed of 10 km/h, respectively.

In the evolved UTRA (UMTS terrestrial radio access) uplink, single-carrier frequency division multiple access (SC-FDMA) radio access was adopted owing to its advantageous low peak-to-average power ratio (PAPR) feature, which leads to wide coverage area provisioning with limited peak transmission power of a set of user equipment (UE). This paper proposes orthogonal pilot channel generation using the combination of FDMA and CDMA in the SC-FDMA-based evolved UTRA uplink. In the proposed method, we employ distributed FDMA transmission for simultaneous accessing users with different transmission bandwidths, and employ CDMA transmission for simultaneous accessing users with identical transmission bandwidths. Moreover, we apply a code sequence with a good auto-correlation property such as a constant amplitude zero auto-correlation (CAZAC) sequence employing a cyclic shift to increase the number of sequences. Simulation results show that the average packet error rate (PER) performance using an orthogonal pilot channel with the combination of FDMA and CDMA in a six-user environment, i.e., four users each with a 1.25-MHz transmission bandwidth and two users each with a 5-MHz transmission bandwidth, employing turbo coding with the coding rate of R = 1/2 and QPSK and 16QAM data modulation coincide well with those in a single-UE environment with the same transmission bandwidth. We show that the proposed orthogonal pilot channel structure using the combination of distributed FDMA and CDMA transmissions and the application of the CAZAC sequence is effective in the SC-FDMA-based evolved UTRA uplink.

In the evolved UTRA (UMTS terrestrial radio access) downlink, orthogonal frequency division multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference and flexible accommodation of different spectrum arrangements. This paper presents the optimum adaptive modulation and channel coding (AMC) scheme for simultaneously assigned resource blocks (RBs) for the same user when frequency and time domain channel-dependent scheduling is used in the downlink OFDMA radio access with single-antenna transmission. Theoretical analyses and simulation results show that, irrespective of the application of power adaptation to RB-dependent modulation, the improvement in the achievable throughput of the RB-dependent modulation scheme compared to that for the RB-common modulation scheme is slight, i.e., 4 to 5%. In addition, the number of required control signaling bits in the RB-dependent modulation scheme becomes greater than that for the RB-common modulation scheme. Therefore, the authors conclude that the RB-common modulation and channel coding rate scheme is preferred, when multiple RBs of the same coded stream are assigned to one user in the case of single-antenna transmission.

This paper proposes physical channel structures and a cell search method for OFDM based radio access in the evolved UTRA (UMTS Terrestrial Radio Access) downlink, which supports multiple scalable transmission bandwidths from 1.25 to 20 MHz, in the proposed physical channel structures, the central sub-carrier of the OFDM signal is located on the frequency satisfying the 200-kHz raster condition regardless of the transmission bandwidth of the cell site. Moreover, the synchronization channel (SCH) and broadcast channel (BCH), which are necessary for cell search, are transmitted from the central part of the entire transmission spectrum with a fixed bandwidth. In the proposed cell search method, a user equipment (UE) acquires the target cell in the cell search process in the initial or connected mode employing the SCH and possibly the reference signal, which are transmitted from the central part of the given transmission bandwidth. Alter detecting the target cell, the UE decodes the common control information through the BCH, which is transmitted at the same frequency as the SCH, and identifies the transmission bandwidth of the cell to be connected. Computer simulations show the fast cell search time performance using the proposed SCH structure and the cell search method.

For high speed orthogonal frequency division multiplexing (OFDM) plus multiple-input multiple-output (MIMO) multiplexing, a new coded layered space-time-frequency (LSTF) architecture with iterative signal processing at the receiver is proposed, where each independent codeword is threaded in the three-dimensional (3D) space-time-frequency transmission resource array. The iterative receiver structure is adopted consisting of a joint minimum-mean-square-error soft-interference-cancellation (MMSE-SIC) detector and the maximum a posteriori (MAP) convolutional decoders. Simulation results show that the proposed LSTF architecture can achieve almost the same performance as the LSTF (i.e., LSTF-a) where coding is applied across the whole information stream. However, due to its structure of multiple parallel lower speed encoders/decoders with shorter codeword length, the proposed LSTF architecture can be more easily implemented than the LSTF-a.

This paper proposes an intra-node B orthogonal pilot channel structure employing a sector-specific orthogonal sequence and cell-specific (node B-specific) scrambling code for orthogonal frequency division multiplexing (OFDM)-based radio access in the E-UTRA downlink. This paper also proposes a sophisticated orthogonal pilot channel employing code division multiplexing (CDM) to separate sectored beams and distributed frequency division multiplexing (FDM) to separate streams (transmission antennas) in MIMO channel transmissions simultaneously. Successive simulation results verify the effectiveness of the proposed orthogonal pilot channel structures using distributed FDM among multiple streams and CDM between sectored beams. Furthermore, the simulation results also show that the average packet error rate (PER) performance using the proposed intra-node B orthogonal pilot channel is significantly improved compared to that of the conventional structure employing a random sequence, particularly for 16QAM and 64QAM modulations under high intra-node B interference-to-desired signal power ratio conditions

This paper compares the user throughput and the sector throughput performance using fast sector selection (FSS) with muting and simultaneous transmission with soft-combining for the intra-node B macro diversity in the downlink OFDM based radio access. System-level simulations show that FSS with muting achieves an approximately 10% higher user throughput for intra-node B macro diversity user equipment (UE) compared to simultaneous transmission with soft-combining, while maintaining almost the same user throughput performance for one-link connection UE assuming the equal served traffic model. Therefore, we conclude that FSS with muting is a more promising candidate than simultaneous transmission with soft-combining as the intra-node B macro diversity scheme in the downlink OFDM based radio access

This paper presents the optimum resource block (RB) bandwidth for frequency and time domain channel-dependent scheduling based on system-level simulations in the downlink orthogonal frequency division multiplexing (OFDM) based radio access. The simulation results clarifies that the optimum RB bandwidth is within the range of approximately 150 to 375 kHz assuming typical power delay profile models in a cellular system such as typical urban, pedestrian-B, and vehicular-A modes, from the viewpoint of the multiuser diversity effect gained in frequency domain channel-dependent scheduling. The results also show that considering the overhead loss by the control signaling bits for scheduling, adaptive modulation and coding and hybrid ARQ with packet combining, the optimal RB bandwidth is in the range of approximately 375 to 750 kHz

This paper proposes frequency and time domain channel-dependent scheduling employing an adaptive transmission bandwidth for the pilot channel for channel quality indication (CQI) measurement in the uplink single-carrier (SC)-FDMA radio access. In the proposed scheme, a high multiuser diversity effect due to frequency domain channel-dependent scheduling is gained by assigning a wide pilot transmission bandwidth to user equipments (UEs) near a cell site, whereas the influence of the CQI measurement error is mitigated by assigning a narrow pilot transmission bandwidth to UEs near the cell boundary at the cost of utilizing multiuser diversity in the frequency domain. System simulation results elucidate that the cell throughput using the adaptive pilot transmission bandwidth with the predetermined threshold, THSINRof -6 dB is increased by approximately 600 kbps compared to that using a fixed 1.25-MHz pilot transmission bandwidth, i.e., only time domain channel-dependent scheduling, owing to an increasing multiuser diversity effect in the frequency domain. We also show that the user throughput using the adaptive pilot channel transmission bandwidth scheme at a 5% cumulative distribution function is increased by approximately 35 and 30% compared to that using a 5-MHz transmission for 16 and 32 UEs per cell, respectively, for the inter-site distance of 500 m

This paper presents field experimental results on real-time 1-Gbps packet transmission using antenna-dependent adaptive modulation and channel coding (AMC) with 4-by-4 MIMO multiplexing using maximum likelihood detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of the surviving symbol replica candidates (ASESS) in the downlink orthogonal frequency division multiplexing (OFDM) radio access. The field experiments, which are conducted at the average moving speed of 30 km/h, show that the real-time packet transmission of greater than 1 Gbps in a 100-MHz channel bandwidth (i.e., 10 bits/second/Hz) is achieved at the average received signal-to-interference plus background noise power ratio (SINR) of approximately 13.5 dB using 16QAM modulation and turbo coding with the coding rate of 8/9, The results also show that the antenna-dependent AMC is very beneficial to improve the measured throughput in a real propagation channel environments, where the average received power associated with each transmitted signal varies with the difference of greater than approximately 6 dB. Finally, we show that the measured throughput of greater than 1 Gbps is achieved employing antenna-dependent AMC at the probability of approximately 98% in a measurement course, where the maximum distance from the cell site was approximately 300 m with the respective transmitter and receiver antenna spacings of 1.5 m and 40 cm with the total transmission power of 10 W

This paper is focused on the study of layered space-time-frequency (LSTF) architectures with channel coding for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing system in high speed wireless transmission under frequency-selective fading channel. In order to achieve the available spatial, temporal and frequency diversity, and at the same time make the system implementation feasible for ultra high data rate OFDM MIMO multiplexing, we propose a new LSTF architecture with each independently coded layer being threaded in the three-dimensional space-time-frequency transmission array. List sphere decoding is used for MIMO multiplexing detection, and the irregular low-density parity-check code (LDPC) is chosen as the channel code. Three construction rules are adopted to generate high coding rate irregular LDPC codes with low encoding complexity and little performance loss. Simulation results show that the proposed LSTF architecture can significantly outperform the LSTF assuming each independently coded layer being transmitted through a permanently assigned antenna, and get almost the same performance as the LSTF applying coding across the whole information stream. On the other hand, due to its structure of multiple parallel lower-speed codecs with shorter codeword length, the proposed LSTF architecture is more realizable for ultra high data rate transmission than the LSTF applying coding across the whole information stream

This paper presents experimental results on real-time packet transmission of greater than 1 Gb/s using 4-by-4 multiple-input-multiple-output (MIMO) multiplexing and maximum-likelihood detection (MLD)-based signal detection with a decreased level of computational complexity in orthogonal frequency-division multiplexing (OFDM) radio access. We apply our previous algorithm called adaptive selection of surviving symbol replica candidates (ASESS) based on the maximum reliability in MLD employing QR decomposition and the M-algorithm (QRM-MLD) to reduce the extremely high level of computational complexity in the conventional MLD. The experimental results using multipath fading simulators are in good agreement with the computer simulation results. The loss in the required received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) is suppressed to within approximately 1-2 dB. Therefore, through experiments, we demonstrate that the QRM-MLD employing ASESS is very beneficial in reducing the influence of hardware implementation loss, as well as in decreasing the required received Eb/N0. We further show that the extremely high-speed real-time packet transmission of greater than 1 Gb/s in a 100-MHz channel bandwidth (i.e., 10 bit/s/Hz) is achieved at the average received Eb/N0per receiver antenna of approximately 12 dB using 16QAM modulation and turbo coding with the coding rate of 8/9 in 4-by-4 MIMO multiplexing

This paper proposes adaptive control of the number of surviving symbol replica candidates, Sm(m denotes the stage index), based on the minimum accumulated branch metric of each stage in maximum-likelihood detection employing QR decomposition and the M-algorithm (QRM-MLD) in orthogonal frequency-division multiplexing with multiple-input-multiple-output (MIMO) multiplexing. In the proposed algorithm, Smat the mth stage (1lesmlesNt, Ntis the number of transmission antenna branches) is independently controlled using the threshold value calculated from the minimum accumulated branch metric at that stage and the estimated noise power. We compared the computational complexity of QRM-MLD employing the proposed algorithm with that of conventional methods at the same average packet error rate assuming the information bit rate of 1.048 Gb/s in a 100-MHz channel bandwidth (i.e., frequency efficiency of approximately 10 bit/s/Hz) using 16QAM modulation and turbo coding with the coding rate of 8/9 in 4-by-4 MIMO multiplexing. Computer simulation results show that the average computational complexity of the branch metrics, i.e., squared Euclidian distances, of the proposed adaptive independent Smcontrol method is decreased to approximately 38% that of the conventional adaptive common Smcontrol and to approximately 30% that of the fixed Smmethod (Sm=M=16), assuming fair conditions such that the maximum number of surviving symbol replicas at each stage is set to Mcirc=16

Orthogonal frequency and code-division multiplexing (OFCDM) systems have been introduced for high-speed data transmission in future wireless mobile communications. In this paper, a hybrid multicode interference cancellation (MCI) and minimum mean-square error (MMSE) detection scheme is presented for the turbo-coded OFCDM systems. Channel estimation based on a code-multiplexed pilot channel is employed. The weights of the hybrid detection are derived theoretically and an effective method to generate the weights in practical applications is proposed. By means of computer simulation, the effects of system parameters on the performance are studied extensively. It is shown that the hybrid detection outperforms pure MMSE detection in various channel conditions, especially for high-level modulation schemes. To carry out interference regeneration for the hybrid detection, the conventional turbo decoding algorithm which only decodes systematic bits should be extended to decode parity bits as well. Moreover, two iterations in turbo decoding are sufficient to provide good performance for the system with the multistage hybrid detection. Finally, given time-domain spreading factor N/sub T/, the system performance improves with frequency-domain spreading factor N/sub F/. However, the frequency diversity gain is saturated when N/sub F/ is large (i.e., N/sub F//spl ges/16).

The orthogonal frequency and code division multiplexing (OFCDM) system with 2-D spreading (time- and frequency-domain spreading) is becoming a promising candidate for future broadband wireless communication systems. OFCDM is more attractive than orthogonal frequency-division multiplexing (OFDM) both by introducing frequency-domain spreading for frequency diversity provision and time-domain spreading for flexible data rate provision. To provide high-speed mobile services, multicode transmission is employed in conjunction with OFCDM. In a Gaussian or flat-fading channel, multicode channels are orthogonal. However, in a realistic wireless channel, the orthogonality no longer maintains. Thus, multicode interference (MCI) is caused. This paper focuses on the investigation of the effect of Doppler shift on the downlink transmission of high-speed mobile OFCDM systems. A practical channel estimation algorithm based on a code-multiplexed pilot channel is employed to track the variations of fading channels. Hybrid MCI cancellation and minimum mean-square error (MMSE) detection proposed by the authors is employed as an efficient way to eliminate the MCI in the frequency domain. The system performance is analytically studied with imperfect channel estimation to show how it is affected by parameters such as the window size in the channel estimation, Doppler shift, the number of stages of the hybrid detection, the power ratio of pilot to data channels, spreading factor, and so on

The broadband orthogonal frequency and code division multiplexing (OFCDM) system with two-dimensional spreading (time and frequency domain spreading) is becoming a very attractive technique for high-rate data transmission in future wireless communication systems. In this paper, a quasianalytical study is presented on the downlink performance of the OFCDM system with hybrid multi-code interference (MCI) cancellation and minimum mean square error (MMSE) detection. The weights of MMSE are derived and updated stage by stage of MCI cancellation. The effects of channel estimation errors and sub-carrier correlation are also studied. It is shown that the hybrid detection scheme performs much better than pure MMSE when good channel estimation is guaranteed. The power ratio between the pilot channel and all data channels should be set to 0.25, which is a near optimum value for the two-dimensional spreading system with time domain spreading factor (N/sub T/) of 4 and 8. On the other hand, in a slow fading channel, a large value of the channel estimation window size /spl gamma/N/sub T/, where /spl gamma/ is an odd integer, is expected. However, /spl gamma/=3 is large enough for the system with N/sub T/=8 while /spl gamma/=5 is more desirable for the system with N/sub T/=4. Although performance of the hybrid detection degrades in the presence of the sub-carrier correlation, the hybrid detection still works well even the correlation coefficient is as high as 0.7. Finally, given N/sub T/, although performance improves when the frequency domain spreading factor (N/sub F/) increases, the frequency diversity gain is almost saturated for a large value of N/sub F/ (i.e., N/sub F/ /spl ges/ 32).

Performances of optimum and minimum mean square error (MMSE) receivers for variable spreading factor orthogonal frequency and code division multiplexing (VSF-OFCDM) systems are compared in this paper. In VSF-OFCDM systems, the existence of multicode interference (MCI) in the frequency domain due to frequency-selective fading channels dramatically degrades the system performance. A quasi-analytic bit error rate performance is presented in the presence of imperfect channel estimations. Numerical results show that with linear computation complexity the MMSE receiver can improve system performance significantly by suppressing the MCI, although it cannot perform as well as the optimum receiver. Thus, with a small number of code channels, an optimum receiver can be employed to achieve better performance, whereas the MMSE receiver is suitable for a system with a large number of code channels due to simple complexity. In addition, the MMSE receiver is more robust than the optimum receiver to the different configurations of system parameters, e.g., spreading factors. Moreover, it is found that pilot channel power should be carefully assigned by making tradeoffs between the channel estimation quality and the received SNR for each code data channel.

The paper proposes an adaptive selection algorithm for surviving symbol replica candidates based on the maximum reliability in ML detection with QR decomposition and M-algorithm (QRM-MLD) for OFCDM MIMO multiplexing. In the proposed algorithm, symbol replica candidates newly-added at each stage are ranked for each surviving symbol replica from the previous stage using multiple quadrant detection. Then, branch metrics are calculated only for the limited number of symbol replica candidates with high reliability based on an iterative loop in increasing order of the accumulated branch metrics from the candidate with the minimum one. Simulation results show that the computational complexity of the proposed algorithm from the viewpoint of the number of real multiplications is reduced to approximately 1/6 and 1/1900, respectively, compared to that of the original QRM-MLD and that of the conventional MLD with squared Euclidian distance calculations for all symbol replica candidates, assuming the identical achievable average block error rate (BLER) performance in 4-by-4 MIMO multiplexing with 16QAM data modulation. The results also show that 1-Gbps throughput is achieved at the E/sub b//N/sub 0/ per receiver antenna of approximately 9 dB using the adaptive selection algorithm in QRM-MLD associated with 16QAM modulation and turbo coding with coding rate of 8/9, assuming a 100-MHz bandwidth for a twelve-path Rayleigh fading channel (rms delay spread, 0.26 /spl mu/sec; maximum Doppler frequency, 20 Hz).

This paper proposes likelihood function generation of complexity-reduced maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) suitable for soft-decision turbo decoding and investigates the throughput performance using QRM-MLD with the proposed likelihood function in multipath Rayleigh fading channels for orthogonal frequency and code division multiplexing (OFCDM) with multiple-input multiple-output (MIMO) multiplexing. Simulation results show that by using the proposed likelihood function generation scheme for soft-decision turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio (E/sub b//N/sub o/) at the average block error rate (BLER) of 10/sup -2/ at a 1-Gbps data rate is significantly reduced compared to that using hard-decision decoding in OFCDM access with 16 QAM modulation, the coding rate of 8/9, and 8-code multiplexing with a spreading factor of 8 assuming a 100-MHz bandwidth. Furthermore, we show that by employing QRM-MLD associated with soft-decision turbo decoding for 4-by-4 MIMO multiplexing, the throughput values of 500 Mbps and 1 Gbps are achieved at the average received E/sub b//N/sub o/ of approximately 4.5 and 9.3 dB by QPSK with the coding rate of R = 8/9 and 16 QAM with R = 8/9, respectively, for OFCDM access assuming a 100-MHz bandwidth in a twelve-path Rayleigh fading channel.

This paper presents field experimental results on an adaptive antenna array-beam forming (AAA-BF) receiver with that uses simultaneous estimations of received timings and direction of arrivals (DOAs) of Rake combining paths employing directive beam reception based on a pilot channel-assisted two-dimensional power profile in the reverse link for broadband DS-CDMA packet wireless access. Laboratory experimental results elucidate that path-independent weight generation is superior to path-common weight generation based on the implemented AAA-BF receiver in a multipath Rayleigh fading channel with up to eight paths. The required average received signal energy per bit-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) using path-common antenna weight generation is increased according to the increase in the angle spread among paths, /spl sigma/, since the antenna gain toward the DOA of each path is reduced. Nevertheless, the increase in the antenna gain according to the number of antennas is achieved by using path-independent antenna weight generation regardless of the /spl sigma/ value up to 20 degrees. Furthermore, the field experimental results show that the required average received signal to interference plus background noise power ratio (SINR) at the average block error rate (BLER) of 10/sup -2/ employing path-independent weight generation is reduced by approximately 3.5 dB compared to that using path-common weight generation for a large r.m.s. angle spread such as 9 degrees. In the field experiments, the required average received SINR at the average BLER of 10/sup -2/ using the AAA-BF receiver with path-independent antenna weight generation is reduced by approximately 6.0 dB compared to that with one-antenna reception, regardless of the angle spread values.

This paper proposes maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) sophisticatedly combined with the multipath interference canceller (MPIC) based on multipath interference (MPI) replica generation exploiting two-dimensional minimum mean squared error (MMSE) for multiple-input multiple-output (MIMO) multiplexing in broadband DS-CDMA. Simulation results clarify that the proposed QRM-MLD coupled with MPIC exhibits excellent signal separation capability by sufficient MPI suppression effect through a three-stage MPIC comprising two-dimensional MMSE, followed by QRM-MLD associated with soft-decision Turbo decoding. We also show that the throughput values of 200,250, and 300 Mbps (corresponding frequency efficiency values are 5.0, 6.0, and 7.5 bits/sec/Hz, respectively) are achieved at the average received signal energy per bit-to-noise power spectrum density ratio (E/sub b// N/sub 0/) of approximately 6.0,9.5, and 13.0 dB by QPSK with the coding rate of R = 8/9, 8PSK with R = 3/4, and 8PSK with R = 8/9, respectively in 4-by-4 MIMO multiplexing, for broadband DS-CDMA assuming a 40-MHz bandwidth in a six-path Rayleigh fading channel with the maximum Doppler frequency of 20 Hz.

The paper investigates the effect of time diversity derived from hybrid automatic repeat request (ARQ) with packet combining considering space and path diversity schemes on variable spreading factor orthogonal frequency and code division multiplexing (VSF-OFCDM) packet wireless access in a downlink broadband multipath fading channel based on laboratory and field experiments. The results show that, for a fixed modulation and channel coding scheme (MCS), time diversity derived from hybrid ARQ is effective in reducing the required received signal-to-interference-plus-noise power ratio (SINR) according to an increase in the number of transmissions, M, up to 10, even when the diversity effects are obtained through two-branch antenna diversity reception and path diversity by a number of multipaths greater than 12 observed in a real fading channel. Meanwhile, in combined use with the adaptive modulation and channel coding (AMC) scheme associated with space and path diversity, we clarify that the gain derived through time diversity is almost saturated at M=4 in chase combining and M=2 in incremental redundancy, since the improvement in the residual packet error rate (PER) obtained through time diversity becomes small owing to the low PER in the initial packet transmission arising from appropriately selecting the optimum MCS in AMC.

This work presents experimental results on fast sector selection (FSS) with entire-bandwidth assignment in the forward link for orthogonal frequency and code division multiplexing (OFCDM) broadband packet access. We first elucidate that the additional improvement derived from FSS with independent frequency-block assignment by taking advantage of frequency-selective fading compared to FSS with entire-bandwidth assignment is small from the viewpoint of the received signal level when the number of frequency-block is not large. Then, we investigate the effect of FSS with entire-bandwidth assignment in laboratory and field experiments considering the application of key techniques for high-speed packet access such as hybrid ARQ with packet combining, soft-decision turbo decoding, and pilot channel-assisted channel estimation. Field experiments, which are conducted in an urban area near Tokyo, show that by applying FSS, the required signal power at the average residual packet error rate (PER) of 10/sup -3/ can be reduced by approximately 2.0 and 1.0 dB compared to the case without FSS when the maximum number of retransmissions in Incremental redundancy is 0 and 1, respectively.

This paper investigates the practical effects of low-rate turbo coding and its soft-decision decoding considering the influence of path timing detection, channel estimation, and pre-decoder level adjustment for broadband packet DS-CDMA in the reverse link in a real multipath Rayleigh fading channel. Field experiments are conducted in an urban environment using the implemented broadband DS-CDMA transceiver at the average vehicular speed of approximately 30 km/h. The experimental results elucidate that accurate path timing detection and channel estimation of each packet frame are achieved by taking advantage of the dedicated pilot channel for the use of low-rate turbo coding (i.e., actual spreading factor value of data channel is nearly one). We clarify that by employing turbo coding with the coding rate of R = 1/8, the required average received signal energy per bit-to-interference plus background noise power spectrum density ratio (E/sub b//I/sub o/) at the average packet error rate (PER) of 10'2 is decreased by approximately 1.0 to 1.5 dB compared to that with R = 1/2. Furthermore, we show that the additional improvements by reducing R to 1/16 are small assuming the same chip rate and employing two-branch antenna diversity reception associated with coherent Rake combining for broadband DS-CDMA with a 40-MHz bandwidth.

This paper proposes variable spreading and chip repetition factors (VSCRF)-CDMA in the reverse link for broadband wireless access, which flexibility supports employing the same air interface both in multi-cell environments such as cellular systems and in isolated-cell environments such as hot-spot areas and indoor offices. In VSCRF-CDMA, the conventional CDMA feature, i.e., time-domain spreading using a combination of cell (or user)-specific scrambling and channelization codes, is applied in a multi-cell environment in order to suppress effectively other-cell interference to utilize one-cell frequency reuse. Meanwhile, in an isolated-cell environment, a chip repetition scheme is used in a part of the time-domain spreading by employing an orthogonal code in order to realize orthogonal multiple access by utilizing a comb-shaped frequency spectrum. Simulation results elucidate that the required average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) using VSCRF-CDMA associated with the combination of spreading factor (SF/sub D/) = 4 and chip repetition factor (CRF) = 4 at the average packet error rate of 10/sup -2/ can be achieved by approximately 6 dB assuming four simultaneous users with the information bit rate of 6.4 Mbps each (the corresponding frequency efficiency becomes 0.62 bps/Hz) in an isolated-cell environment in a three-path Rayleigh fading channel with two-branch antenna diversity reception.

We recently proposed broadband packet wireless access based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the forward link and variable spreading and chip repetition factors (VSCRF)-CDMA in the reverse link for the systems beyond IMT-2000. This paper presents experimental evaluations on the throughput performance of that proposed broadband packet wireless access scheme associated with adaptive modulation and channel coding (AMC) in a multipath Rayleigh fading channel employing the implemented base station (BS) and mobile station (MS) transceivers. The implemented OFCDM transceiver verifies the effectiveness of the combination of the OFCDM and AMC including QPSK and 16QAM data modulations with a fast round trip delay of 6 msec for improving the throughput performance by exploiting the frequency diversity effect in a broadband channel. The experimental results show that the throughput performance of 100 and 200 Mbps employing AMC is achieved at the average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) of approximately 7.5 and 19 dB, respectively, for 15-code multiplexing for the spreading factor of SF=16 in the OFCDM forward link with a 100-MHz bandwidth, in a six-path fading channel with the fading maximum Doppler frequency of f/sub D/=20 Hz. Furthermore, we elucidate that the peak throughput of 20 Mbps is achieved at the average received E/sub s//N/sub 0/of approximately 9 dB by employing QPSK data modulation with R = 1/2 for three-code multiplexing for SF= 4 in a four-path fading channel in the broadband CDMA reverse link with a 40-MHz bandwidth.

This paper experimentally investigates the throughput performance employing hybrid automatic repeat request (ARQ) with a packet combining algorithm, i.e.. incremental redundancy and Chase combining, from the viewpoints of the achievable throughput satisfying the required residual packet error rate (PKR), coupled with real-time adaptive modulation and channel coding (AMC) operation, for variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM) broadband wireless access in a forward-link multipath fading channel. Since the implemented base station (BS) and mobile station (MS) transceivers can achieve a high peak throughput of greater than 100 Mbps, the time diversity effect by packet combining or code combining in hybrid ARQ is thoroughly examined associated with the frequency diversity effect over a broadband channel and antenna diversity reception. The experimental results demonstrate that even in a six-path Rayleigh fading channel, incremental redundancy is superior to Chase combining under high Doppler frequency conditions such as f/sub D/ = 140 Hz, especially when the number of maximum retransmissions is small, because the larger coding gain after code combining is effective in compensating for packet errors due to inappropriate modulation and coding scheme (MCS) selection caused by the tracking error of the AMC loop for the fast fading variations. Furthermore, it is elucidated that the throughput values of 7 Mbps and 10 Mbps (achieved at the average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s/M/sub 0/) of approximately -5 dB) satisfying the required PER of below 10/sup -4/ are achieved when the maximum number of retransmissions is approximately 3 and 7, respectively, in the six-path fading channel with f/sub D/ = 20 Hz.

This paper proposes a new fast packet-scheduling algorithm based on instantaneous received signal-to-inference power ratio (SIR) with a constraint condition that assures a minimum throughput (minimum throughput assured instantaneous SIR (MTA-ISIR) method hereafter) and investigates its throughput performance in high-speed downlink packet access (HSDPA). In the proposed algorithm, packet transmission is assigned with priority based on the instantaneous received SIR for users with a larger average received SIR than the prescribed threshold value, and packet transmission is fairly assigned to users who have smaller average SIR than the threshold value by raising the instantaneous SIR corresponding to the threshold value. Computer simulation results elucidate that the number of high-rate users with a user throughput more than 2-Mbps employing the proposed MTA-ISIR method is increased by approximately 1.9 (1.5) times that using the proportional fairness method while maintaining a similar level of fairness for low-rate users when the threshold value is 18 dB in a 2(1)-path Rayleigh fading channel.

This paper proposes broadband packet wireless access employing Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) with two-dimensional spreading that prioritizes time domain spreading in the forward link and multi-carrier/DS-CDMA (MC/DS-CDMA) in the reverse link for the system beyond IMT-2000. Based on the wireless access scheme, we propose major radio air interfaces in the physical layer to achieve our target maximum throughput beyond 100 Mbps and 20 Mbps in the forward and reverse links, respectively. Furthermore, we present key technologies such as the adaptive radio link parameter control coupled with link adaptation, pilot channel assisted coherent detection in both links, adaptive antenna array beam forming transmitter and receiver, cell search, and channel coding. Finally, simulation results elucidate that VSF-OFCDM using die proposed radio link parameters achieves a throughput above 100 Mbps at the average received signal energy per symbol-to-background noise power spectrum density ratio (Ea/No) of approximately 13 dB (101.5 MHz bandwidth, without antenna diversity reception, 12-path Rayleigh fading channel). Furthermore, MC/DS-CDMA realizes a throughput above 20 Mbps at the average received Ea/No of approximately 8 dB (40 MHz bandwidth, with antenna diversity reception, 6-path Rayleigh fading channel).

This paper proposes a three-step cell search algorithm for a multi-carrier (MC)-CDMA broadband packet wireless access system with a 50-100 MHz bandwidth and evaluates the cell search time performance in a numerous-multipath fading channel. To achieve fast cell search, we introduce a continuously transmitted synchronization channel (SCH), which is multiplexed into sub-carriers with equal sub-carrier spacing and scrambled by the code common to all cell sites, and a common pilot channel (CPICH), which is continuously-transmitted in both the time and frequency domains and scrambled by a cell specific scrambling code (CSSC). In the proposed three-step algorithm, fast Fourier transform (FFT) window timing and packet frame timing are successively detected by using a guard interval and SCH and then, the CSSC of the target cell is identified by CPICH. Furthermore, in the proposed method, since the CSSC identification is performed for several candidates of the FFT window and packet frame timings, the best cell having the least path loss is precisely obtained despite the channel load, ie, the number of dedicated traffic channels (DTCH) in each cell. Computer simulation results show that by using the three-step cell search algorithm, the cell detection probability of 90% is achieved within approximately 77 msec (44 msec) when the number of DTCH with the information bit rate of 2 Mbit/s of each cell is distributed with the average of 20 and the standard deviation of 15 (0), when the FFT symbol-correlation of the SCH is averaged over N/sub PST//sup SCH/ = 20 (4) frames in the second step and the CPICH symbol-correlation is coherently averaged during N/sub CST//sup CPICH/ = 16 (10) symbols along the time axis and N/sub CSF//sup CPICH/ = 8 sub-carriers along the frequency axis CS-F in the third step.

Based on laboratory experiments, the paper investigates the multiuser interference suppression effect of the coherent adaptive antenna array diversity (CAAAD) receiver. An optical fiber feeder is employed in the intermediate frequency (IF) stage of a base transceiver station (BTS), aiming at the practical use of adaptive antenna array beamforming techniques in the W-CDMA air interface. We employ a configuration in which the optical fiber conversion, i.e., electrical-to-optical (E/O) or O/E conversion, is performed on a received signal amplified by an automatic gain control (AGC) amplifier in the IF stage in order to abate the impact of the noise component generated by the E/O (O/E) converters. We first show by computer simulation the superiority of the optical fiber conversion in the IF stage to that in the radio frequency (RF) stage from the viewpoint of reducing the bit error rate (BER) performance. Furthermore, experimental results elucidate that the loss in the required transmit signal energy per bit-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) of the implemented CAAAD receiver at the average BER of 10/sup -3/ employing the optical fiber feeders in the IF stage compared to that with coaxial cables is within a mere 0.2 dB for conditions of 6 antennas, 3 users, 2-path Rayleigh fading channel model, and the ratio of the target signal energy per bit-to-interference power spectrum density ratio (E/sub b//I/sub 0/) of the desired user to that of the interfering users for fast transmission power control is /spl Delta/E/sub b//I/sub 0/ = -15 dB.

This paper presents coherent adaptive antenna array beamforming (CAAA-BF) combined with maximal ratio combining (MRC) diversity techniques (space diversity, SD, or polarization diversity, PD) and evaluates the interference suppression effect of these methods under multipath fading in the W-CDMA reverse link. Computer simulation results show that even when the number of active users is 150 (note that the capacity normalized by the processing gain, Pg, is 78%), the required transmit signal energy-per-bit-to-background-noise power spectrum density ratio (E/sub b//N/sub 0/) at the average block error rate (BLER) of 10/sup -2/ with CAAA-BF with 2-branch SD reception, i.e., 4 antennas per branch, is decreased by approximately 1.4 dB compared to that with CAAA-BF using 8 antennas. These results indicate that by combining CAAA-BF with diversity techniques, although the interference suppression effect is slightly decreased compared to that with CAAA-BF using the identical number of antennas in an interference-limited channel, due to the broadening beam width, there is a significant additional space diversity effect especially when the number of resolved paths is small.

The paper presents the throughput performance when employing hybrid automatic repeat request packet combining, i.e., Chase combining and incremental redundancy, in forward-link orthogonal frequency and code division multiplexing (OFCDM) broadband packet wireless access achieving a peak throughput above 100 Mbps. Simulation results elucidate that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) of 4 dB and 10 dB, employing incremental redundancy, is increased by approximately 50% and 70% in a 12-path exponentially decayed fading channel compared to that using Chase combining for QPSK and 16QAM data modulation, respectively. However, we show that despite the superiority of incremental redundancy to Chase combining in the achievable throughput for the respective modulation and coding schemes (MCSs), the total throughput when employing incremental redundancy associated with a near optimum MCS set in an actual adaptive modulation and coding (AMC) operation becomes almost identical to that using Chase combining in a low maximum Doppler frequency, f/sub D/, channel. Finally, we show that incremental redundancy coupled with a higher channel coding rate is still more effective than Chase combining in improving the throughput for a high f/sub D/ channel owing to its large coding gain.

This paper compares by computer simulation the achievable throughput performance employing fast packet scheduling algorithm focusing on the throughput of each user in high speed downlink packet access (HSDPA). Three packet scheduling algorithms are employed: the maximum carrier-to-interference power ratio (CIR), proportional fairness (PF), and round robin (RR) methods. Simulation results elucidate that although the maximum CIR method achieves an aggregated user throughput within a cell higher than that using the PF and RR methods, the PF method is advantageous because it enhances the user throughput for a large number of access; users with a lower received signal-to-interference power ratio (SIR), who an located outside the normalized distance of 0.6-0.7 from a cell site (this corresponds to the area probability of 50-60% within the cell) compared to the maximum CIR method. Finally, we show that the average user throughput in a 2-path Rayleigh fading channel is reduced by approximately 30% compared to that in a 1-path channel due to severe multipath interference (MPI) and that the average user throughput is strongly affected by the total traffic produced within a cell, which is directly dependent on the number of users within a cell and the data size per packet call.

This paper elucidates the optimum bandwidth per subcarrier in the reverse link for multicarrier (MC)/DS-CDMA using a 10 to 80 MHz bandwidth in a multipath fading channel with numerous resolved multipaths, taking into account all major effects, ie, the improvement in the Rake time diversity effect and the degradation in the path search and the channel estimation due to multipath interference (MPI). The simulation results show that the improvement in radio link performance is almost saturated at a bandwidth of greater than 40 MHz (the corresponding number of multipaths is 12-48) when the spreading factor of the channel is SF = 32, and the best performance is achieved at the bandwidth of approximately 20 MHz when SF = 4 with two-branch antenna diversity reception. This is generated by the tradeoff between the improvement in the Rake time diversity effect and the increased MPI in addition to the degradation in the path search and channel estimation accuracy associated with a lower average received signal-to-interference plus background noise power ratio. Therefore, we conclude that MC/DS-CDMA, where each carrier has the bandwidth of approximately 20-40 MHz, is one of the most promising candidates for broadband packet wireless access in the reverse link.

This paper proposes an adaptive radio parameter control scheme that utilizes the maximum number of retransmissions in hybrid automatic repeat request (ARQ) in addition to the data modulation and channel coding scheme (MCS) according to quality of service (QoS) requirements and propagation conditions such as the delay spread in the forward link of orthogonal frequency and code division multiplexing (OFCDM) broadband wireless access. We elucidate that for non-real time (NRT) class data transmission, it is appropriate to employ three MCSs, QPSK with the coding rate of R = 1/2, 16QAM with R = 1/2 and 3/4. Application of a much higher MCS set. 16QAM with R = 5/6 and 64QAM with R = 3/4, in addition to the three MCSs improves the throughput under much higher average received E/sub s//N/sub 0/ conditions in a short-delay spread environment. Meanwhile, for real time (RT) data transmission assuming the number of retransmissions of M = 2, it is appropriate to use five MCSs, QPSK with R = 1/3, 1/2 and 16QAM with R = 1/3, 1/2, and 3/4. Thus, we elucidate that the appropriate MCS associated with the maximum number of retransmissions, i.e., major radio parameters should be controlled according to the QoS requirements and the propagation channel conditions. Furthermore, the proposed adaptive radio parameter control scheme that considers the QoS requirements is unified by controlling the threshold value for selecting the appropriate MCS associated with the maximum number of retransmissions in the hybrid ARQ.

This paper compares by computer simulation the throughput performance of a multipath interference canceller (MPIC) and that of a sliding-window chip equalizer (SWCE) in high-speed downlink packet access (HSDPA) in a multipath fading channel. We also propose new MPIC and SWCE configurations that suppress not only multipath interference (MPI) of the downlink shared channel (DSCH) in its own cell but also the multiuser interference (MUI) of the DSCH from a neighboring interference-dominant cell. Computer simulation results elucidate that when the MPIC or the SWCE which suppresses the MPI of the DSCH in only its own cell is employed, the MPIC achieves throughput greater than that of the SWCE ranging from a lower (i.e., the lower average received E/sub b//N/sub 0/) to a higher throughput such as 4.8 Mbit/s, which is achieved by the modulation and coding scheme (MCS) of 16QAM with coding rate R = 1/2. In an even higher throughput region, achieved using the MCS of 16QAM with R = 3/4, the SWCE exhibits superiority over MPIC. Furthermore, we also clarify that with the MPIC and the SWCE with neighboring-cell MUI suppression, the SWCE achieves better throughput compared to the MPIC.

This paper proposes a pilot channel assisted minimum mean square error (MMSE) combining scheme in orthogonal frequency and code division multiplexing (OFCDM) based on actual signal-to-interference power ratio (SIR) estimation and investigates the throughput performance in a broadband channel with a near 100-MHz bandwidth. In the proposed MMSE combining scheme, the combining weight of each sub-carrier component is accurately estimated from the channel gain, noise power, and transmission power ratio of all the code-multiplexed channels to the desired one, by exploiting the time-multiplexed common pilot channel in addition. to the coded data channel. Simulation results elucidate that the required average received signal energy per bit-to-noise spectrum density ratio (E/sub b//N/sub 0/) for the average packet error rate (PER)=10/sup -2/ is improved by 0.6 and 1.2 dB by using the proposed MMSE combining Instead-of the conventional equal gain combining (EGC) in a 24-path Rayleigh fading channel (exponential decay path model, maximum delay time is approximately 1 /spl mu/sec) in an isolated cell environment, when the number of multiplexed codes = 8 and 32, respectively, with the spreading factor of 32. Furthermore, when the average received E/sub b//N/sub 0/=10 dB, the achievable throughput, i.e., the number of simultaneously multiplexed codes for the average PER=10/sup -2/ in the proposed MMSE combining, is increased by approximately 1.3 fold that of the conventional EGC.

Multicode code division multiple access (CDMA) is a new transmission scheme for flexible and high-speed data communications. The basic idea of multicode CDMA, is to assign multiple channelization codes to any given user. If these channel codes are orthogonal, the self-interference among them can be eliminated in an additive white Gaussian noise (AWGN) channel. However, in a multipath environment, these intrauser signals from different delay paths no longer maintain orthogonality and, thus, cause interference, i.e., multicode interference (MCI), to each other. In high-speed data networks, where the number of users is much less than in the voice networks, the MCI may represent a large portion of the total interference and has a great impact on the system performance. A complex spreading multicode wideband CDMA receiver with RAKE structure and multistage MCI cancellation is studied. By pilot aided channel estimation, the MCI associated with the reference user is regenerated and subtracted from the received signal by a cancellation factor of /spl lambda/. A complete and consolidated theoretical analysis is presented to show that the system performance is significantly improved by the MCI cancellation. The optimal cancellation factor in the kth stage is approximated by /spl lambda//sub opt//sup (k)//spl les/1-2P/sub e//sup (k-1)/, where P/sub e//sup (k-1)/ the error probability of the (k-1)th stage. The optimal value of each stage can be chosen from 0.5 to 0.85 for a wide range of signal to noise ratios.

This paper proposes a multipath interference canceller (MPIC) associated with orthogonal code-multiplexing that achieves much higher peak throughput than 2 Mbit/s with adaptive data modulation for high-speed packet transmission in the wideband direct sequence-code division multiple access (W-CDMA) forward link, and evaluates its throughput performance by computer simulation. The simulation results elucidate that sufficient multipath interference (MPI) suppression is achieved by a four-stage MPIC with 6-12 orthogonal code-multiplexing using one iterative channel estimation with pilot and decision feedback data symbols and further that the interference rejection weight control according to the number of observed multipaths is effective in improving the throughput. It is also demonstrated that MPIC exhibits a superior MPI suppression effect to a chip equalizer in the lower received signal energy per bit-to-background noise spectrum density (E/sub b//N/sub 0/) channel around 0-3 dB owing to the successive channel estimation at each stage. We show that the maximum peak throughput using MPIC is approximately 2.1 fold that without MPIC in a two-path and three-path Rayleigh fading channel and that the peak throughput of 8.0 Mbit/s is achieved using 64 QAM data modulation in a two-path fading channel within a 5 MHz bandwidth. Furthermore, the required average E/sub b//N/sub 0/ for satisfying the same throughput with MPIC is decreased by more than 2.0 dB.

A three-stage coherent multistage interference canceller (COMSIC) employing pilot symbol-assisted (PSA) channel estimation for replica generation of multiple access interference (MAI) is implemented and its performance in the presence of frequency selective multipath fading is experimentally evaluated by a multipath fading simulator. A fast transmission power control (TPC) method suitable for COMSIC is also proposed, in which the signal-to-interference plus background noise power ratio (SIR) at the matched filter (MF) based RAKE receiver is measured to achieve a short TPC delay and the target signal-to-interference ratio value is compensated by an outer loop so that the measured block error rate (BLER) is equal to the prescribed target value. The experimental results show that as expected the COMSIC satisfactorily reduces the MAI even when the number of active users is equal to the spreading factor in a multipath fading environment, and thus, improves the bit error rate (BER) performance in a multiuser environment. The results also show that the proposed fast TPC method with a two-slot delay associated with COMSIC works satisfactorily and the combination of COMSIC and fast TPC significantly decreases the transmission power of a mobile station (required transmission power of a mobile station with COMSIC at the average BER of 10/sup -3/ is decreased by approximately 2.0 (3.0) dB compared with the MF-based RAKE receiver with (without) antenna diversity reception). This extends the cell coverage, battery life, and increases the system capacity in the reverse link.

Multicode CDMA is a new transmission scheme for flexible and high-speed data communications. In a multipath environment, these intra-user multicode signals from different delay paths no longer maintain their orthogonality, thus causing significant interference, i.e. multicode interference (MCI), to each other. A multicode CDMA receiver with RAKE structure and multi-stage MCI cancellation is proposed. By pilot aided channel estimation, the MCI associated with the reference user is regenerated and subtracted from the received signal. The detailed receiver structure is presented and theoretical analysis is given to show that the system performance is significantly improved by the MCI cancellation. It is shown that the optimal cancellation factor in the k-th stage can be approximated by /spl lambda//sub opt//sup (k)//spl les/1-2P/sub e//sup (k-1)/, where P/sub e//sup (k-1)/ is the error probability of the (k-1)th stage.

This paper proposes a new parallel-type coherent multistage interference canceller (COMSIC) coupled with multiple-antenna reception (MA-COMSIC) and evaluates the capacity increase in a multipath fading channel in the DS-CDMA reverse link, in order to improve further the channel estimation accuracy and increase the space diversity effect. Simulation results show that the MA-COMSIC with a two block-wise antenna configuration, in which each block has 3 antennas (we denote as (B, D) = (2, 3)), achieved a lower required transmit E/sub b//N/sub 0/ than that with (B, D) = (1, 6) except for extreme cases such as when the number of simultaneous users K exceeds 120 corresponding to K/Pg = 250% (where Pg is the processing gain of 48 = 16/spl times/3). Consequently, even when K = 120, the increase in the required transmit E/sub b//N/sub 0/ of MA-COMSIC with (B, D) = (2, 3) from that in a single-user case is only 1.0 dB owing to the significant improvement in the channel estimation accompanied by the diversity effect. We also elucidate that even when the angle spread among constituent waves in the same path is /spl sigma//sub /spl Lambda/S/ = 5 degrees, the loss of the required transmit E/sub b//N/sub 0/ with (B, D) = (2, 3) for the ideal fading correlation case is suppressed to within 0.5 dB.

This paper proposes a multipath interference canceller (MPIC) that employs soft-decision replica generation combined with hybrid ARQ (HARQ) to achieve a peak throughput of more than 10 Mbps in a multipath fading environment in the W-CDMA forward link. In the proposed scheme, more accurate multipath interference (MPI) replica generation is possible by decreasing the influence of data-decoding errors associated with the reliability of the originally transmitted and retransmitted packets. Simulation results elucidate that by applying the soft-decision replica, a four-stage MPIC improves the peak throughput by approximately 300 kbps and 1 Mbps with 64QAM data modulation in an average equal level 2- and 3-path Rayleigh fading channel compared with the MPIC using the hard-decision replica, respectively. In addition, by effectively combining the originally transmitted packet with the identical retransmitted one in soft-decision MPI replica generation, the throughput performance is further improved by approximately 300 kbps in a 3-path environment. Consequently, we clarify that the maximum peak throughput using the proposed MPIC achieves approximately 11.8 and 10.4 Mbps with 64QAM data modulation in a 2- and 3-path Rayleigh fading channel, respectively, within a 5 MHz bandwidth.

This paper proposes a new fast transmit power control algorithm for forward link inter-cell site diversity, called site independent diversity transmit power control (hereafter SIDTPC) and compares the effect of decreasing the total transmit signal energy per bit-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) of all cell sites for three methods: SIDTPC, site selection diversity transit power control (SSDT), and conventional TPC during inter-cell site diversity (hereafter CTPC) in the W-CDMA forward link. The SIDTPC method differs from SSDT in that each cell site transmits a dedicated physical channel (DPCH) with different transmit power, which is adaptively weighted according to the path loss between each cell site and a mobile station (MS), that is to say, with larger (smaller) transmit power for the cell having the smaller (larger) path loss, resulting in a decreased total transmit power similar to the SSDT method, while maintaining a superior feature which enables SIDTPC to be less sensitive to the reception errors of the control bits sent via the reverse link. Simulation results demonstrated that when the traffic ratio of voice service to data service is 1:1, the required total average transmit E/sub b//N/sub 0/, at the average block error rate (BLER) of 10/sup -2/ for 50% of MSs using the SIDTPC method is decreased by approximately 0.4 (0.5) dB and 2.0 (0.2) dB compared to those with the CTPC and SSDT methods, respectively, for Doppler frequency, f/sub D/, of 5 (80) Hz.

In order to increase the link capacity in the wideband direct sequence code division multiple access (W-CDMA) reverse link, employing a parallel-type coherent multistage interference canceller (COMSIC) is more practical than using a serial (successive)-type due to its inherent advantage of a short processing delay, although its interference suppression effect is inferior to the serial-type. Therefore, this paper proposes a parallel-type COMSIC with iterative channel estimation (ICE) using both pilot and decision-feedback data symbols at each canceling stage. Computer simulation results show that the required average transmit E/sub b//N/sub 0/ for obtaining the average BER of 10/sup -3/ using the three-stage parallel-type COMSIC with ICE using pilot and decision-feedback data symbols after forward error correction (FEC) decoding (number of iterations was 2 at each stage) was decreased by approximately 2.1 dB compared to a COMSIC with channel estimation using only pilot symbols, with the spreading factor (SF) of 16 and when the number of active users was 20 (thereby the capacity normalized by the processing gain (Pg) becomes 42%). The results also show that the required average transmit E/sub b//N/sub 0/, loss of the parallel-type COMSIC using ICE at the average BER of 10/sup -3/ compared to the serial-type was negligible (i.e., within 0.2 dB) due to the significantly improved channel estimation and decreased data decision error, while achieving a much shorter processing delay irrespective of the number of active users.

The combined effect of coherent RAKE combining using the weighted multislot averaging (WMSA) channel estimation filter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K=2 WMSA channel estimation filter reduces the required E/sub b//I/sub 0/ at the average BER of 10/sup -3/ by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E/sub b//I/sub 0/ is minimized when the SIR measurement interval is M=10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results obtained in an area nearby Tokyo showed that the average BER of 10/sup -3/ is achieved at the target E/sub b//I/sub 0/ per antenna of approximately 2.5 dB by using four-finger branch RAKE and two-branch antenna diversity. Although the target E/sub b//I/sub 0/ to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent RAKE combining and fast TPC works well in practical multipath fading channels.

In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) from high rate users. A four-antenna pilot symbol-assisted coherent adaptive antenna array diversity (PSA-CAAAD) receiver comprising an adaptive antenna array based on a minimum mean squared error (MMSE) criterion and a RAKE combiner is implemented in preliminary laboratory and field experiments. There are two important design concepts of the PSA-CAAAD receiver. The first is that the adaptive antenna array forms an antenna beam for each resolved propagation path and tracks only slow changes in the directions of arrival (DOAs) and average powers of the desired and interfering user signals. The second is that the RAKE combiner tracks the instantaneous changes in channel conditions and coherently combines the signals of the desired user propagating along the resolved paths to maximize the instantaneous signal-to-interference plus background noise power ratio (SINR). This paper presents, both by laboratory and field experiments, the effectiveness of PSA-CAAAD receiver as a powerful means to reduce severe MAI from high rate users, and that it is more effective than using a space diversity receiver with the same number of antennas in the W-CDMA reverse link.

A 3-stage coherent multistage interference canceller for DS-CDMA mobile radio was implemented and its performance in a frequency selective multipath fading channel is experimentally evaluated by using a multipath fading simulator. The implemented interference canceller applied pilot symbol-assisted channel estimation for data decision and replica generation of multiple access interference (MAI). The laboratory experiment demonstrated that, as is expected, the coherent multistage interference canceller can reduce the MAI to satisfactory levels in a multipath fading environment and thus, improving the bit error rate (BER) performance under multiuser environment.

Coherent DS-CDMA forward and reverse links periodically transmitting pilot symbols every data slot to estimate the fading channels are considered; Np-pilot systems are placed at the beginning of each data slot. A pilot symbol-assisted channel estimation scheme that uses weighted multi-slot averaging (WMSA) is presented for coherent RAKE combining. The BER performance achievable by WMSA coherent RAKE combining is evaluated by computer simulations under multipath Rayleigh fading environments and compared with those of other channel estimation methods. For the DS-CDMA reverse link, fast transmit power control (TPC) based on measured signal-to-interference plus noise ratio (SINR) is employed so the simulation also considers fast closed loop TPC. It is demonstrated by computer simulations that the required signal energy per bit-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) can be reduced by about 0.8 dB compared to RAKE combining using simple linear interpolation and that the E/sub b//N/sub 0/ loss from the ideal channel estimation is as small as 0.5 dB both with and without antenna diversity. The BER performance achievable by the time multiplexed pilot is also compared with that of the parallel pilot channel.

Multiple-symbol differential detection (DD) with reference signal estimation based on the feedback of past detected symbols is presented for differentially encoded 16-level amplitude/phase shift keying (16DAPSK). A suboptimal decision is derived. The approximate analysis of the bit-error rate (BER) performance taking into account the decision error propagation effect is presented in an additive white Gaussian noise (AWGN) channel and the BER performance is compared with those of 16DPSK and 16 quadrature amplitude modulation (16QAM).