Joint channel-physical layer network coding in multi-way wireless relay systems

Multi-way relaying is a widely considered network configuration, where multiple communication nodes exchange their information via a single relay. In this configuration, a pairwise information exchange and a channel condition based node pair selection for simultaneous information transfer provide the best performance. For such schemes, the relationship between the minimum number of time slots required for complete information exchange among communication nodes and the number of communication nodes is derived. Furthermore, this paper proposes an improved joint channel decoding-network coding algorithm, which is to be employed at the relay node. In the proposed joint decoding algorithm, the soft information of the information bits is exchanged between the channel decoders corresponding to different node pairs transmitting simultaneously. We also propose three different schemes for soft information exchange between the different channel decoders. The proposed algorithm is highly scalable with respect to the number of communication nodes. Simulation results demonstrate that our proposed joint decoding algorithm offers improved error performance over the existing joint decoding algorithms for a three-way relay system under the three different information exchanging schemes. The simulation results verify that the performance of the proposed decoding algorithm increases with the number of overlapping information pairs

Distributed beamforming techniques for dual-hop decode-and-forward MIMO relay networks

Cooperative relay networks with multiple antennas at each node enable achieving both macro diversity and micro diversity in a wireless fading channel. Using beamforming along with space-time (ST) coding at the source and the relay of a cooperative relay network allows achieving both diversity gain and array gain. In this paper we propose novel distributed beamforming techniques for a space-time (ST) coded dual-hop cooperative multiple-input multiple-output (MIMO) decode-and-forward (DF) relay network to minimize the pair-wise error probability (PEP), while maintaining the SNR at the relay node above a given threshold. Beamforming techniques for the availability of full-instantaneous channel state information at the transmitter (CSIT) as well as statistical CSIT are proposed. The source and the relay compute their own beamforming matrices based only its own CSIT subject to individual power constraints at each node. The simulation results show that the proposed beamforming techniques offer a significant performance enhancement over the performance of a relay network using ST coding only. Furthermore, the proposed beamforming techniques maintain their performance improvement throughout the possible spatial correlation factor range for the channel.5 page(s

Transmit beamforming techniques for space-frequency coded MIMO-OFDM systems in a correlated Ricean fading channel

In highly spatially correlated channels the diversity gain achieved by space-frequency (SF) coding is significantly low. Nevertheless, when full or partial channel state information is available at the transmitter, improved performance can be obtained by combining transmit beamforming with SF coding. In this paper we propose two novel transmit beamforming techniques based on the minimum pair-wise error probability (PEP) criterion for SF-coded MIMO-OFDM systems in frequency-selective Ricean fading channels. The proposed beamforming techniques (referred to as Technique 1 and Technique 2) require only the channel mean and spatial correlation statistics. Technique 1 optimally distributes the total transmit power among all the eigenmodes of the channel, whereas Technique 2 allocates the total transmit power only to the strongest eigenmodes of the channel. The simulation results demonstrate that Technique 1 and 2 offers considerable performance improvements over a system using only SF coding in low and highly spatially correlated channels, respectively. When compared with Technique 1, Technique 2 is more appealing due to the facts that it has less computational complexity, and that it offers better performance in highly correlated channels for all values of the Ricean-K factor.5 page(s

Space-Time Coded Uplink Transmission with

In this paper, we consider the application of spacetime (ST) block coding in the uplink of DS-CDMA systems. A novel system architecture, which is the combination of singlecarrier time-reversal zero-padded (SC-TR-ZP) based ST block coding with chip-interleaved block-spread (CIBS)-CDMA, is proposed for frequency-selective uplink transmissions. Moreover, several decision feedback sequence estimation (DFSE) schemes are proposed for ST coded CIBS-CDMA systems. The simulation results demonstrate a significant improvement in the performance of the proposed system compared to CIBS-CDMA without ST coding. The simulation results also indicate that a substantial performance improvement can be achieved either using multistage modified unwhitened DFSE (MMUDFSE) or whitened DFSE (WDFSE) scheme over the linear MMSE equalizer. Furthermore, a low-complexity linear prediction (LP) based approach can be adapted to compute the whitening prefilter required in WDFSE to transform the system model into its minimum phase equivalent. I

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 4, NO. 6, NOVEMBER 2005 3095 Space--Time-Coded CDMA Uplink Transmission

The problem of adopting space--time block coding (STBC) in the uplink of direct sequence code division multiple access (DS-CDMA) systems is addressed. A novel system architecture is proposed for space--time (ST)-coded uplink transmissions over multipath fading channels with multiple user interference (MUI)-free reception. This proposed system is a combination of single-carrier time-reversal zero-padding (SC-TR-ZP)-based STBC with chip-interleaved block-spread (CIBS)-CDMA. Simulation results show that a substantial performance improvement can be achieved by adopting ST coding compared to the original CIBS-CDMA scheme without ST coding. Optimal maximum likelihood sequence estimation (MLSE) may be computationally prohibitive for long channels and/or with high-level modulation. Hence, the performance of different decision feedback sequence estimation (DFSE) schemes is investigated for the proposed ST-coded uplink system. In the case of whitened DFSE (WDFSE), a linear prediction (LP)-based approach is adapted for designing a whitening prefilter. Furthermore, a new scheme, which is a combination of linear equalization (LE) and modified unwhitened DFSE (MUDFSE) is proposed. The proposed combined LE--MUDFSE (Comb. LE--MUDFSE) scheme is very attractive as error-floor behavior appearing in other unwhitened DFSE schemes is eliminated. The simulation results indicate that a substantial performance improvement over the minimum mean-square error (MMSE) equalizer can be achieved by using either Comb. LE--MUDFSE scheme or WDFSE scheme

Wireless Communications: Trends and Challenges

Abstract — Emerging demands for high data rate services and high spectral efficiency are the key driving forces for the continued technology evolution in wireless communications. Third generation (3G) mobile communication systems have already been commercially deployed in certain parts of the world to meet the initial demand for high data rate packet-based services including wireless internet access. Recently, several advancements have been introduced for 3G wireless systems to further improve the data rate and the system performance (e.g., high speed downlink packet access (HSDPA) in wideband code division multiple access (WCDMA) systems, 1x evolution-data and voice (1xEV-DV) in cdma2000 systems). Nevertheless, due to rapid growth of wireless multimedia services, it is apparent that 3G wireless systems will be unable to comply with the ever increasing demand for broadband wireless services. As a result, even before widespread commercial deployment of 3G wireless systems, the standardization process of the next generation wireless communication systems (namely, fourth generation (4G) or beyond 3G (B3G) systems) has already been initiated. The next generation broadband wireless systems are expected to support variety of services requiring different data rates and different QoS (quality of service) levels. Obviously, the key feature of 4G (or B3G) systems over growing 3G systems is the feasibility of much higher data rate services. In this paper, an overview of leading technological advances that enable broadband wireless capabilities and state-of-the-art research in various aspects of wireless communication is presented. The topics include multipleinput multiple-output (MIMO) systems, cooperative diversity, ultra wideband (UWB), cross-layer design, QoS provisioning, cognitive radio and wireless security. I