Singlecarriercyclicprefix(SCCP) modulation has been adopted as one of the physical layer air-interfaces for IEEE802.I6 standards due to its less stringent requirement onpeak-to-averagepowerratio(PAPR) than multicarrier modulation. As a single carrier transmission, however, the received SCCP blocks suffer from inter-symbol interference (ISI). Theblockiterativegeneralizeddecisionfeedbackequalizer(BI-GDFE) is an effective interference cancellation scheme which generally shows performance improvement over linear equalizers. However, in order to achieve a significant gain, the channel must contain rich multipath components, and this may not necessarily be true in many systems. In this paper, we propose to applycyclicdelaydiversity(CDD) to a SCCP system so that the possible performance improvement by using a BI-GDFE detector can be enhanced. The asymptotic performance of the proposed system is analyzed using random matrix results. We propose a scheme to determine the optimal delay parameter for CDD. Computer simulations have shown that by incorporating CDD into the transmitter and using a BI-GDFE receiver, the BER performance of the system can approach the MFB within several iterations for high SNR region.

In this letter, we propose a low complexity algorithm for extended turbo product codes by considering both the encoding and decoding aspects. For the encoding part, a new encoding scheme is presented for which the operations of looking up and fetching error patterns are no longer necessary, and thus the lookup table can be omitted. For the decoder, a new algorithm is proposed to extract the extrinsic information and reduce the redundancy. This new algorithm can reduce decoding complexity greatly and enhance the performance of the decoder. Simulation results are presented to show the effectiveness of the proposed scheme.

We address the issue of delay selection for cyclic delay diversity (CDD) for single carrier cyclic prefix (SC-CP) transmissions over correlated clustered channel and detected using the BI-GDFE. Due to the correlation among the transmit antennas, beamforming is used to generate uncorrelated virtual channels for the application of CDD using the generalized transmit MMSE method. As the BI-GDFE can exploit the frequency diversity present, judicious selection of the cyclic shifts would improve the performance of system. Delay selection is performed by finding the delays which minimizes the variance of the even order channel statistics, and using these delays will yield the best performance. Computer simulations are presented to show the effectiveness of the delay selection scheme for the considered system.

We present a downlink single carrier cyclic prefix transmission method which employs directional beamforming and artificial delay for channels with dominant cluster paths. The proposed technology robustly manages the overall delay of the transmission channel for performance gain. For channels with delays larger than the cyclic prefix, the proposed method shortens the delay for IBI-free transmission. When the cyclic prefix duration exceeds that of the channel duration, the proposed technique can lengthen the effective channel delay to possibly improve the system's performance. Computer simulations are presented to verify the efficacy of the proposed transmission technology.

In multiuser OFDMA uplink, different users usually have different carrier frequency offsets (CFOs). Estimation of these multiple CFOs is a crucial and challenging task. In this paper, a dedicated pilot OFDM symbol is designed to estimate the CFOs. Based on the maximum likelihood (ML) principle, a method is derived to estimate the CFOs of all users by optimizing a multi-dimensional (MD) cost function. To reduce complexity, the MD optimization problem is turned into independent one-dimensional (ID) optimization problems based on a specially designed pilot OFDM symbol. It is proved that the CFOs are identifiable by optimizing the ID cost functions. Although the ID optimization is substantially simpler than the MD optimization, it may still be vulnerable to local minima/maxima and sometimes too complex for wireless applications. A fast algorithm is then derived, which finds the CFOs in closed forms and needs very low computational complexity.

This paper addresses the problem of signal detection for a single carrier cyclic prefix (SC-CP) system. As a single carrier transmission, the received SC-CP blocks suffer from intersymbol interference (ISI). Although it is possible to deploy linear equalizers to mitigate the ISI, their performance is usually far away from the matched filter bound (MFB). The block iterative generalized decision feedback equalizer (BI-GDFE) is an effective interference cancellation scheme which generally shows performance improvements over linear equalizers. However, in order to achieve a significant gain, the channel must contain rich multipath components, and this may not necessarily be true in many systems. By applying cyclic delay diversity (CDD) to a SC-CP system, the frequency diversity of the system can be improved, and thus, the possible performance improvement by using a BI-GDFE detector is also enhanced. Computer simulations have shown that by incorporating CDD into the transmitter and using a BI-GDFE receiver, the BER performance of the system can approach the MFB within several iterations for high SNR region.

Efficient estimations of the carrier frequency offset (CFO) and channel are vital to orthogonal frequency division multiplexing (OFDM). In this paper, a new method based on limited channel length and null subspace is proposed to estimate the CFO in OFDM. The method needs only one OFDM block (symbol) as pilot. The identifiability of the method is analyzed and requirements for the pilot are found. The same pilot is also used for channel estimation. It is shown that a pilot with constant amplitude and random phases is the best choice for both channel and CFO estimation. Furthermore, an enhanced method is proposed by using multiple receiving antennas. Simulations demonstrate that the proposed methods are effective.

In this paper, we study the design and decoding schemes for shortened turbo product codes adopted in IEEE 802.16 standard. To design a good structure for shortened turbo product code, we compute the undetected error probability of the component codes and select the optimal generator polynomials in terms of their undetected error probability. For the decoding algorithm, we present an efficient Chase decoding algorithm for shortened turbo product codes in which the reliability factor used in Pyndiah's scheme is not needed. Thus the decoding complexity is reduced greatly by avoiding the normalization operation of the whole codeword at each iteration. Simulation results are presented to verify the performance of the proposed algorithm

We present an iterative chip-level time domain equalizer (TEQ) for direct sequence code division multiple access (DS-CDMA) downlink with code multiplexed training symbols. For heavily loaded system, the multiple access interference (MAI) may be so severe that the pilot information offered by the training symbols are badly distorted. And this results in poorly converged equalizer coefficients. The proposed approach does not only utilize the training symbols, put also all the active and passive spreading codewords for TEQ adaptation. At each iteration, improved estimates of the transmitted data symbols are acquired and together with the pilot symbols, they are used to train the TEQ weights. Consequently, the signal-to-interference and noise (SINR) ratios of the effective training symbols is increased. Simulation results show that the proposed equalizer can achieve better bit-error rate performances than the generalized minimum mean squared error equalizer.

In this paper, we consider the performance enhancement of signal detection for single carrier-cyclic prefix (SC-CP) transmissions over correlated multiple inputs single outputs (MISO) channels. The block-iterative generalized decision feedback equalizer (BI-GDFE) receiver is used to combat the effect of intersymbol interference (ISI). While BI-GDFE outperforms linear equalizers, the improvement could be limited if the channel does not contain a high degree of frequency-selectivity. On the other hand, direct application of cyclic delay diversity (CDD) to a highly correlated MISO channel generally cannot increase the frequency diversity significantly. In this paper, we propose combining eigen-beamforming and CDD for frequency diversity enhancement, with which the performance of the BI-GDFE is also greatly improved. Computer simulations show that the proposed system not only offers diversity improvement but also beamforming gain. It is also observed that the BER performance of the proposed system can approach its matched filter bound (MFB)

In TD-SCDMA downlinks, one favorable receiver structure is the single user detection, based on block linear equalization (SUD-BLE), implemented by fast Fourier transform (FFT). In this paper, we first analyze the interference involved with the sub-block processing proposed in (I. Held et al, Proc. China Wireless Congress, 2002) and then propose a new sub-block processing receiver for fast time-varying channels. The proposed receiver consists of two stages. In the first stage, the entire data chip block is first partitioned into overlapping sub-blocks and they are then equalized and despread. We then artificially generate the interference caused by adjacent blocks and unwanted chip interference within the same sub-block and subtract the interference from the received data signal. Then a second sub-block processing is performed to detect the transmitted symbols. Simulation results show that the proposed receiver provides significant performance improvement as compared with the conventional sub-block processing previously proposed.

This paper presents a polynomial-based generalized recursive least squares channel estimator for the dispersive Rayleigh fading channel. The estimator is formulated using a state transition matrix based on polynomial prediction instead of autoregressive modelling, and does not require channel statistics to operate. Analytical and simulated mean square deviation results for the tracking performance of the estimator are presented. The results show that by selecting appropriate values of the "forget factor" and polynomial order, the estimator performs almost as well as the optimal Kalman estimator even in fast fading.

This letter presents a simple polynomial predictor-based sequence detector for the Rayleigh nonselective fading channel. Unlike the polynomial predictor-based sequence detector proposed by Borah and Hart, the new receiver is not restricted to constant envelope modulation schemes. Analytical and simulated results are presented. In some instances, the proposed receiver performs within 6 dB of the equivalent maximum-likelihood sequence estimation receiver.

This paper presents a simple polynomial predictor based sequence detector for the nonselective fading channel. Although the estimator used in the receiver is mathematically similar to the one presented by Borah and Hart (see IEEE Trans. Commun., vol.47, p.862-73, 1999), the implementation is much simpler. Instead of requiring matrix operations and recursions, the proposed estimator is simply a bank of FIR filters. Unlike the polynomial predictor based sequence detector (PPSD) of Borah and Hart (see IEEE Trans. Commun., vol.47, p.360-64, 1999), it is not restricted to constant envelope modulation schemes.

This paper presents a simple DPSK receiver for the frequency-selective fading channel. The channel is modelled as an f-power series truncated to the first two terms. Two time invariant receiver filters are used to remove the channel induced ISI and to separate the two implicit diversity branches. The received samples from each branch are then differentially decoded and combined. Analytical and simulation results for binary DPSK show that this receiver out performs the conventional receiver using matched filtering and a product demodulator.

A maximum likelihood sequence estimator for the dispersive Rayleigh fading channel is developed. Following previous work, the MLSE uses a Kalman based channel estimator to acquire the channel parameters necessary to formulate the maximum likelihood metric. However, unlike the MLSE receiver presented previously, the proposed receiver uses the f-power series channel model to formulate the ML metric and the state space representation of the channel and the received samples. For channels with small delay spreads, this approach is advantageous because only a small number of parameters are required to be estimated by the Kalman channel estimator. Simulation results are presented for various channel parameters.

A simple technique for removing intersymbol interference (ISI) introduced by "linearly frequency-selective" fading channels is presented. The technique involves the optimization of the overall impulse response of the transmit and receive filters and effectively reduces the channel to one which is flat fading. Computer simulation results show that this equalization method works for channels with small delay spreads.

An adaptive receiver is presented in this paper for the reception of linearly modulated signals transmitted over a time- and frequency-selective fading channel. The channel is modeled as a truncated power series which represents the dispersive fading channel as a sum of three elementary flat-fading channels. The proposed receiver consists of a sequence estimator with a parallel channel estimator. The channel estimator recovers the instantaneous fading processes associated with each elementary channel and filters them to generate one-step predictions of each fading process. Some implementation difficulties and solutions are also discussed. Computer simulations using quadrature phase-shift keying (QPSK) and channels with moderate delay spreads and fade rates have been used to evaluate the performance of the receiver. The results show that our technique has potential in channels with delay spread of about 20%, signal-to-noise ratio (SNR) greater than 15 dB, and applications requiring bit-error rates (BER's) less than 10/sup -2/.