The characterization for the coverage and performance of RF transceiver is an important step in wireless network design. We present that the enhanced receiver sensitivity utilizing an external LNA and improved transmit power can extend the coverage to meet the achievable performance in the real radio environment.

In this paper, high performance MAC is designed and implemented to support multi-gigabit nomadic access systems. New algorithms and Control channels are introduced for low MAC latency and high MAC throughput. The new multi-gigabit nomadic/local area wireless access, called NoLA, is implemented using the proposed MAC. NoLA demonstrated the multi-gigabit service with full HD video streams where the proposed high performance MAC supports the 84 full HD video streams in real time. The implemented NoLA system shows near 1.8Gbps MAC throughput, which can meet the requirements of the gigabit IMT-Advanced wireless nomadic access. It is proved that the proposed high performance MAC used in NoLA can be one of the promising solutions for the future multi-gigabit wireless communication systems.

In this paper, we propose a low complexity MIMO detection method for double space-time block (D-STBC) coded OFDM system. The proposed MIMO detector involves two step decoding process to efficiently de-correlate spatially-multiplexed / space-time-coded signals. The proposed MIMO detector collects feedback information from interfering spatial domain. Then, interference cancellation is applied once to reduce latency. A unique QR decomposition with partial maximum likelihood detection scheme is developed to lower computational complexity while performance is significantly improved. From computer simulation results, our scheme in D-STBC OFDM system outperforms previously proposed iterative detectors based on turbo equalization principle.

In this paper, a new IMT-Advanced wireless communication system employing the proposed MAC frame structures was implemented and demonstrated. The proposed MAC frame structures are designed to provide Gbps data service under the nomadic environment. The implemented system provided near 1.8Gbps MAC throughput. It is shown that the implemented system with the proposed MAC frame structures can meet IMT-Advanced wireless access requirements and it is one of the promising solutions for the future multi-gigabit wireless communication systems.

A MIMO decoding algorithm utilizing poly- diagonalization and tail-biting trellis is proposed. Linear MIMO decoding, such as zero-forcing equalization, is a channel diagonalization technique, where all interferences from other data streams are suppressed for separate decoding. It is well known, however, that such decoders suffer from the noise enhancement. In the proposed scheme, interferences are partially allowed, in order to alleviate the noise enhancement and, then, post trellis decoding is used for the joint detection utilizing the poly-diagonal structure of the effective channel. Under the proposed framework, the zero-forcing equalizer can be regarded as special cases of poly-diagonalization, i.e., of the first order. And the proposed scheme can provide a tradeoff between the complexity and performance by choosing an appropriate order of poly-diagonalization. According to the simulation results, considerable gain can be obtained even with the second order, i.e., bi-diagonalization, for which the decoding complexity is far less than that of the maximum likelihood decoding.

In this paper, we propose a new MIMO algorithm for giga-bps data transmission. To reduce computational complexity and the decoding latency, a 3-stage receiver algorithm, namely multi-rate QR-MDD is proposed. The MIMO receiver consists of multi-dimensional detection, partial interference cancellation and the weighted zero-forcing equalization, where transmit antennas are divided into two group. The first group is transmitted using lower modulation level and lower code rate and the MDD (multi-dimensional detection) algorithms is used for demodulation and decoding, while the second group is transmitted using higher modulation order and higher code rate and the WZF algorithms is used. Once the first group is decoded, they are cancelled out from received signal for demodulation and decoding of the second group. The complexity and the error rate performance are investigated and compared with MLD (Maximum Likelihood Detection) and ZF (zero forcing). The error performance is slightly worse performance than that of MLD. And computational complexity viewpoint of the required number of real multiplications is approximately 2 times the complexity level of ZF.

A MIMO detection algorithm utilizing poly- diagonalization and tail-biting trellis is proposed. Linear MIMO detection, such as zero-forcing or minimum mean squared error (MMSE) equalization, is basically a channel diagonalization technique, where interferences from other data streams are decoupled for the separate decoding. It is well known, however, that such decoders suffer from noise enhancement, which causes considerable performance degradation. In this paper, we propose poly-diagonalization of the channel matrix in zero-forcing and MMSE senses. The idea behind poly-diagonalization is to allow interferences partially in order to alleviate the noise enhancement and, then, to use post trellis decoding for the joint detection utilizing the poly-diagonal structure of the effective channel. Under the proposed framework, the zero-forcing and the MMSE equalizer can be regarded as special cases of poly-diagonalization, i.e., of the first order. The proposed scheme can provide a tradeoff between the complexity and performance by choosing an appropriate order of poly-diagonalization. According to the simulation results, considerable gain can be obtained even with the second order, i.e., bi-diagonalization, for which the decoding complexity is far less than that of the maximum likelihood decoding.

In this paper, we propose an efficient low complexity MIMO detection method for double space-frequency block coded (D-SFBC) OFDM system. The proposed MIMO detector involves three-step filtering process to efficiently de-correlate spatially-multiplexed / space-frequency-coded signals without direct matrix inversion process. As the proposed MIMO detector takes advantage of frequency selectivity, not a favorable channel condition for SFBC system, performance degradation caused by low correlation between two consecutive subcarriers is compensated by assigning weighting factor for every subcarriers in frequency domain. From computer simulation results, our scheme in D-SFTD outperforms previously proposed suboptimal MIMO detection methods such as iterative interference cancellation based V-BLAST.

In this paper, we describe the implementation and validation of the next generation wireless local area network (WLAN) physical (PHY) layer transceiver using a dual-band and multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) scheme. The maximum data rate of the designed system is 270Mbps in 40MHz bandwidth and 2 streams mode. It uses 2 transmit and 3 receive antennas due to reasonable complexity and performance. For implementation and verification of this system, we set up the design flow. To reduce the design time, we propose intermediate design steps which use conventional C language by devising a few rules for hardware description. The system performance is measured from the generated C simulator. We implement all circuits in a single chip

In this paper, a receiver algorithm for an 8times8 MIMO system is considered for Giga-bps data transmission, in which the decoding complexity and latency are crucial factors for implementation of MIMO system with large number of transmit and receive antennae. To reduce computational complexity and the decoding latency, a 3-stage receiver algorithm is proposed. The MIMO receiver consists of multi-dimensional detection, partial interference cancellation and the weighted zero-forcing equalization, where the transmit antennae are divided into two group. The first group is encoded by a lower rate code and multi-dimensional search algorithm is used for demodulation and decoding, while the second group is encoded by higher rate code and weighted zero-forcing equalization is used. Once the first group is decoded successfully, they are cancelled out from the received vector for the decoding of the second group. The complexity and the error rate performance are investigated and compared with a well-known sphere decoding algorithm.

In this paper, we propose a design methodology of low-density parity check (LDPC) code for very high speed transmission. To support various code rates with reasonable hardware and, possibly, the type-II hybrid automatic repeat request (HARQ), a row-splitting/combining method is employed in conjunction with shortening. In row-splitting approach, a parity check matrix of a high rate mother LDPC code, saying rate 5/6, is designed first and then successively row-split the mother matrix to obtain lower rate codes. Shortening provides us another degree of freedom for rate and frame length flexibility for concatenation with MIMO system. The code performance is investigated in terms of frame error rate and compared with those of the LDPC code proposed in IEEE 802.16e standard.

Previously, there has been no report on implementation effort to integrate LDPC encoder and decoder into a single hardware. In this paper, we propose a simple yet low complex systematic LDPC encoding method for class of quasi-cyclic low-density parity-check (QC-LDPC) codes to let LDPC encoder acquire an interchangeable structure, exploited in the decoder. With the proposed encoding scheme, implementation of the proposed encoder becomes much more hardware efficient than having a separate hardware due to LDPC encoder and decoder resource sharing. Moreover, the overall computational complexity of the proposed encoding scheme is lower than the well-known Richardson's efficient encoding scheme (A.T.J. Richardson and R.L. Urbanke, 2001).

In this paper, we propose a simple yet low complex systematic LDPC encoding method for class of quasi-cyclic low-density parity-check (QC-LDPC) codes which have an efficient encoding/decoding algorithm due to the simple structure of their parity-check matrices. The proposed encoding method is applicable to parity-check matrices having dual-diagonal parity structure with single column of weight 3. Unlike finding a direct solution for parity bits in schemes (Richardson and Urbanke, 2001 and Classon and Blankeship, 2004), the proposed scheme first generates arbitrary parity bits. Then, given the parity bits for the first sub-block and exploiting the dual-diagonal structure, all parity bits are found through correction. With slight modification of parity-check matrix H, proposed LDPC encoding scheme is directly applicable to matrices defined in IEEE physical layer standards with almost negligible performance loss. Moreover, the overall computational complexity involving encoding process is lower than well-known Richardson's efficient encoding scheme (Richardson and Urbanke, 2001).

In this paper, we propose an efficient low complexity MIMO detection method for double space-frequency transmit diversity (D-SFTD) based coded OFDM system. The proposed MIMO detector involves three-step filtering process to efficiently de-correlate spatially-multiplexed and space-frequency-coded signals without direct matrix inversion process. As the proposed MIMO detector takes advantage of frequency selectivity, not a favorable channel condition for SFBC system, performance degradation caused by low correlation between two consecutive subcarriers is compensated by assigning weighting factor per subcarrier. From computer simulation results, our scheme in D-SFTD outperforms previously proposed suboptimal MIMO detection methods such as iterative interference cancellation based V-BLAST.

The performance of a receiver front-end limits the quality and range of the given communication link. An appropriate design based on well-defined system parameters and architecture can make a huge difference in the performance, cost and marketability of the entire system. In particular, there is a need for improved digital automatic gain control (AGC) for use in multi input multi output orthogonal frequency division multiplexing (MIMO-OFDM) systems with application to wireless local area networks (WLANs), targeted for the upcoming 802.11n standard based in H. Yu et al. (2004) and H. Yu et al. (2005). In this paper, we propose an efficient algorithm and implementation of the digital AGC for next generation WLANs. The proposed AGC algorithm has two feedback loops for gain control to improve convergence speed, and at the same time maintains the stability of the AGC circuit. Also, a complete set of parameters for practical implementation is obtained by various experiments with fixed point constraints and accuracy requirements.

In this paper, the robust time and frequency offset tracking algorithms and architecture for high throughput wireless local area network (WLAN) systems are presented. The designed architecture has feedback and feed forward compensation loop with well defined loop filter coefficients obtained by various experiments for practical implementation. Considered functional blocks include residual CFO estimator, carrier phase estimator, and timing error estimator. In addition to the algorithm descriptions of these blocks, the implementation method is presented, as they are modeled in the floating/cycle and bit true fixed point C model. These C models have been used as a reference for RTL coding and its verification. The design has been implemented successfully on an FPGA device. The proposed tracking method produces results very close to that of the offset-free system.

In this paper, we describe the design and verification of the next generation wireless local area network (WLAN) physical (PHY) layer transceiver using a dual-band and multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) scheme. The maximum data rate of the designed system is 243 Mbps in 40 MHz bandwidth and 2 streams mode. It uses 2 transmit and 3 receive antennas due to reasonable complexity and performance. For implementation and verification of this system, we set up the design flow. To reduce the design time, we propose intermediate design steps which use conventional C language by devising a few rules for hardware description. The system performance is measured from the generated C simulator. We implement all circuits in Xilinx FPGAs.

In this paper, we describe a FPGA implementation of MIMO detector for future wireless communication system with application to wireless LAN, targeted for upcoming 802.11n standard. The MIMO detector assumes 2 transmit and 3 receive antennas. In soft-output demapper, we apply channel state information which effectively weights reliability information to soft-decision output bits for enhanced link-level performance. The implementation complexity is significantly reduced by avoiding repeated pseudo-inverse calculation for interference cancellation of every received symbol vector. Furthermore, the overall processing time and fabrication area it takes can be significantly reduced by applying bit reduction technique.

For higher data rate wireless communication, multiple antenna and orthogonal frequency division multiplexing (OFDM) schemes are considered as a key technology. In IEEE 802.11 TGn (Task Group n), multiple input multiple output-OFDM (MIMO-OFDM) methods, including spatial division multiplexing (SDM), are adopted for a higher throughput solution in the next generation wireless local area network (WLAN) physical (PHY) layer. In this paper, we design a transmission architecture based on dual-band and MIMO-OFDM schemes and media access control (MAC) layer using the enhanced distributed channel access (EDCA) including a block acknowledgement (ACK) method. Moreover, test results of this prototype system implemented with field programmable gate arrays (FPGA) are introduced.

This paper presents a high accuracy and low complexity timing offset estimation algorithm for multi input multi output orthogonal frequency division multiplexing (MIMO-OFDM) receivers in the tracking mode. First of all we propose an effective architecture of phase tracking for MIMO-OFDM receivers. Then we describe two timing offset estimation algorithms; pilot-aided and CFO-aided timing offset estimation. The first algorithm is a timing phase estimation that can minimize the effect of distorted scattered pilots due to severe fading. We show that the performance of the proposed pilot-aided timing offset estimation very close to that of an offset-free system. The second algorithm attempts to use the computation result of carrier frequency offset estimation in order to reduce complexity. The proposed CFO-aided timing offset estimation has very low complexity comparable to that of the pilot subcarrier aided schemes without performance degradation

In this paper, we propose a multicarrier CDMA approach for forward link PDCH (forward packet data channel) of cdma2000 1xEV-DV which inherits the same architecture and bandwidth. The system utilizes the bandwidth efficient iterative technique (J. Kim et al., 2002) to recover cyclicity of OFDM symbol, and hence it has no cyclic prefix in frame structure for backward compatibility to the existing 1xEV-DV system. We report that the link-level performance of our system is significantly better than previous equalizer-based systems (J.S. Lee and L.E. Miller, 1998) (J.A.C. Bingham, 1990) in frequency selective fading channels

Multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is regarded as a promising technology enabling higher data rate wireless communications in frequency selective fading channels. This paper proposes the next generation wireless local area network (WLAN) physical (PHY) layer transmission technology using dual-band and MIMO-OFDM schemes and media access control (MAC) layer based on the enhanced distributed channel access (EDCA) scheme. Also it shows test results of MIMO-OFDM prototype system implemented with field programmable gate arrays (FPGA). This design targets over 200 Mbps of the maximum PHY data rate in 40 MHz

Multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is regarded as a promising technology enabling higher data rate wireless communications in frequency selective fading channels. This paper proposes the next generation wireless local area network (WLAN) physical (PHY) layer transmission technology using dual-band and MIMO-OFDM schemes. It describes a design of the higher data rate WLAN system targeting the maximum speed of 144 Mbps in 20 MHz bandwidth channels and 288 Mbps in 40 MHz. Additionally, the design suggests a new frame structure based on the 802.11a frame format for guaranteeing the compatibility with IEEE 802.11a legacy-OFDM systems and the MIMO channel estimation capability. For a cost-effective implementation and improved error performance, 2 transmit and 3 receive antennas are used in dual-band.

A new carrier phase and frequency recovery scheme is proposed for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The algorithm uses an extended Kalman filter (EKF) to estimate the instantaneous phase and frequency offset. A linear minimum mean squared error (LMMSE) data-channel extractor is used to isolate the phase and frequency dependent term from the received signal. The proposed algorithm can provide both phase and carrier frequency recovery and has lower complexity than other approaches in the literature. In addition there is very little latency associated with the proposed approach. Simulation results show that the proposed algorithm can track quickly carrier phase and frequency offset and the performance loss compared to the synchronous case is very small.

A decision feedback equalizer (DFE) type of equalization scheme is proposed to mitigate the effect of delay spread for orthogonal frequency division multiplexing (OFDM) systems. The performance degradation is severe in case that the delay spread of wireless channels is longer than a cyclic prefix (CP) due to the effect of inter-symbol interference (ISI) and inter-carrier interference (ICI). The effect of ICI and ISI is analytically described in matrix equations which includes signal-to-noise ratio (SNR) degradation for a given channel condition. The proposed scheme improves the performance using decision feedback mechanism without increasing the length of CP, which preserves the system efficiency for the OFDM.

It is well known that conventional detectors of direct sequence-code division multiple access systems are interference-limited. Multiuser detection has been considered as a promising approach to combat this problem. Since an optimal multiuser detector is too complex to implement, several suboptimal multiuser detector techniques have been developed. The one-shot linear decorrelating detector (LDD) was proposed to reduce the computational complexity and delay required in the conventional LDD, but it still require high complexity. Another one-shot LDD with low complexity was proposed. To improve its performance, this detector uses a maximal ratio combining (MRC) at the two outputs of the left piece of the present bit and the right piece of the next bit in an one-shot window; this detector is called as a one-shot LDD with post-MRC. In spite of the aid of MRC, the performance of the one-shot LDD with post-MRC is worse than the one-shot LDD. To overcome this problem, we propose the one-shot LDD with pre-SDC/post-MRC that employs selection diversity combining (SDC) with multiple antenna elements in front of the one-shot LDD with post-MRC. In asynchronous random code division multiple access systems over fading channels, the largest signal-to-noise ratio (SNR) of SDC, near-far resistance (NFR) of the one-shot LDD, and the output SNR of MRC are random variables. We derive the probability density functions (PDFs) for these random variables and calculate the bit error rate) of the proposed detector using the obtained PDFs. In a comparison of mathematical analysis and computer simulation results, we observe good agreement.

The one-shot linear decorrelating detector (LDD) was proposed to reduce the computational complexity and delay required in the conventional LDD, but it still requires high complexity. Another one-shot LDD with low complexity was proposed. To improve its performance, this detector uses maximal ratio combining (MRC) at the two outputs of the left piece of the present bit and the right piece of the next bit in a one-shot window. In spite of the aid from MRC, the performance of the one-shot LDD with post-MRC is worse than the one-shot LDD. To overcome this problem, we propose a one-shot LDD with pre-SDC/post-MRC that employs selection diversity combining (SDC) with multiple antenna elements in front of the one-shot LDD with post-MRC. In asynchronous random CDMA systems over fading channels, the largest SNR of SDC, near-far resistance (NFR) of the one-shot LDD, and the output SNR of MRC are random variables. We derive the probability density functions (PDFs) for these random variables and calculate the bit error rate (BER) of the proposed detector using the obtained PDFs. In comparison of mathematical analysis and computer simulation results, we observe good agreement.