Abstract — This paper presents a simple two-branch transmit diversity scheme. Using two transmit antennas and one receive antenna the scheme provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit antenna, and two receive antennas. It is also shown that the scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M. The new scheme does not require any bandwidth expansion any feedback from the receiver to the transmitter and its computation complexity is similar to MRRC. Index Terms—Antenna array processing, baseband processing, diversity, estimation and detection, fade mitigation, maximalratio combining, Rayleigh fading, smart antennas, space block coding, space–time coding, transmit diversity, wireless communications. I.

Multiple-antenna systems that operate at high rates require simple yet effective space-time transmission schemes to handle the large traffic volume in real time. At rates of tens of bits/sec/Hz, V-BLAST, where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet V-BLAST suffers from its inability to work with fewer receive antennas than transmit antennas---this deficiency is especially important for modern cellular systems where a basestation typically has more antennas than the mobile handsets. Furthermore, because V-BLAST transmits independent data streams on its antennas there is no built-in spatial coding to guard against deep fades from any given transmit antenna. On the other hand, there are many previously-proposed space-time codes that have good fading resistance and simple decoding, but these codes generally have poor performance at high data rates or with many antennas. We propose a high-rate coding scheme that can handle any...

This paper presents an overview of recent progress in the area of multiple-input–multiple-output (MIMO) space–time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space–time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards.

Transmitter diversity and down-link beamforming can be used in high-rate data wireless networks with orthogonal frequency division multiplexing (OFDM) for capacity improvement. In this paper, we compare the performance of delay, permutation and space--time coding transmitter diversity for high-rate packet data wireless networks using OFDM modulation. For these systems, relatively high block error rates, such as 10%, are acceptable assuming the use of effective automatic retransmission request (ARQ). As an alternative, we also consider using the same number of transmitter antennas for down-link beamforming as we consider for transmitter diversity. Our investigation indicates that delay transmitter diversity with quaternary phase-shift keying (QPSK) modulation and adaptive antenna arrays provides good quality of service (QoS) with low retransmission probability, while space--time coding transmitter diversity provides high peak data rates. Down-link beamforming together with adaptive ante...

We consider transmission using N transmit and reception using M receive antennas in a wireless environment assuming that neither the transmitter nor the receiver knows the channel coefficients. For the scenario that the transmission employs non-coherent T Nunit space-t codes and for a block fading channel model wherete channel is st during T channel uses and varies from T channel usest ot1 ot we est1x- tt bound r # min(T - N,N) ont diversit y advantx1 rM provided byt code. Wet showt0 t requirement r # min(T - N,N) cannot be relaxed by constx-1 for any given R, N , T and r # min(T -N,N),unit T Nspace-t0 codes of rat Rt0 guarant e diversit y adantage rM. Two constructions are given that are also amenable to simple encoding and non-coherent maximum likelihood decoding algorithms.

In this paper, the effect of spatial diversity on the throughput and reliability of wireless networks is examined. Spatial diversity is realized through multiple independently fading transmit/receive antenna paths in single-user communication and through independently fading links in multiuser communication. Adopting spatial diversity as a central theme, we start by studying its information-theoretic foundations, then we illustrate its benefits across the physical (signal transmission/coding and receiver signal processing) and networking (resource allocation, routing, and applications) layers. Throughout the paper, we discuss engineering intuition and tradeoffs, emphasizing the strong interactions between the various network functionalities.

Space-time convolutional codes, that provide maximum diversity and coding gain, are produced for cases with PSK modulation and various numbers of states and antennas. The codes are found

Space-time convolutional codes have shown considerable promise for providing improved performance for wireless communication through combined diversity and coding gain. However, systematic design procedures for space-time convolutional codes have not yet been developed. To date, the few existing example space-time codes have been developed using hand design. Systematic design procedures are presented here, which are based on a few theorems addressing necessary and sufficient conditions on spacetime codes which achieve maximum diversity gain. Other theorems provide methods for calculating and bounding coding gain. A new simple, but highly useful, measure of coding gain is also suggested which can augment existing measures. The use of a possible design procedure is illustrated and new codes are provided which outperform all existing space-time convolutional codes of similar complexity. Keywords space-time coding, space-time modulation, transmit diversity, convolutional coding. This pa...

Space-time communications can help combat fading and, hence, can significantly increase the capacity of ad hoc networks. Cooperative diversity or virtual antenna arrays facilitate spatio-temporal communications without actually requiring the deployment of physical antenna arrays. Virtual MISO entails the simultaneous transmission of appropriately encoded information by multiple nodes to effectively emulate a transmission on an antenna array. We present a novel multilayer approach for exploiting virtual MISO links in ad hoc networks. The approach spans the physical, medium access control and routing layers, and provides 1) a significant improvement in the end-to-end performance in terms of throughput and delay and 2) robustness to mobility and interference-induced link failures. The key physical layer property that we exploit is an increased transmission range due to achieved diversity gain. Except for space-time signal processing capabilities, our design does not require any additional hardware. We perform extensive simulations to quantify the benefits of our approach using virtual MISO links. As compared to using only SISO links, we achieve an increase of up to 150 percent in terms of the end-to-end throughput and a decrease of up to 75 percent in the incurred endto-end delay. Our results also demonstrate a reduction in the route discovery attempts due to link failures by up to 60 percent, a direct consequence of the robustness that our approach provides to link failures.

Abstract — Space-time communications can help combat fading and hence can significantly increase the capacity of ad hoc networks. Cooperative diversity or virtual antenna arrays facilitate spatio-temporal communications without actually requiring the deployment of physical antenna arrays. Virtual MISO entails the simultaneous transmission of appropriately encoded information by multiple nodes to effectively emulate a transmission on an antenna array. We present a novel multi-layer approach for exploiting virtual MISO links in ad hoc networks. The approach spans the physical, medium access control and routing layers and provides: (a) a significant improvement in the end-to-end performance in terms of throughput and delay and, (b) robustness to mobility and interference induced link failures. The key physical layer property that we exploit is an increased transmission range due to achieved the diversity gain. Except for space-time signal processing capabilities, our design does not require any additional hardware. We perform extensive simulations to quantify the benefits of our approach using virtual MISO links. As compared to using only SISO links, we achieve an increase of up to 150 % in terms of the end-to-end throughput and a decrease of up to 75 % in the incurred end-to-end delay. Our results also demonstrate a reduction in the route discovery attempts due to link failures by up to 60%, a direct consequence of the robustness that our approach provides to link failures. I.