Kampol Woradit

Outage behavior of selective relaying schemes

Cooperative diversity techniques can improve the transmission rate and reliability of wireless networks. For systems employing such diversity techniques in slow-fading channels, outage probability and outage capacity are important performance measures. Existing studies have derived approximate expressions for these performance measures in different scenarios. In this paper, we derive the exact expressions for outage probabilities and outage capacities of three proactive cooperative diversity schemes that select a best relay from a set of relays to forward the information. The derived expressions are valid for arbitrary network topology and operating signal-to-noise ratio, and serve as a useful tool for network design.

Outage Behavior of Cooperative Diversity with Relay Selection

Cooperative diversity is a useful technique to increase reliability and throughput of wireless networks. To analyze the performance gain from cooperative diversity, outage capacity is an important figure of merit that captures the inherent diversity-multiplexing trade-off in cooperative diversity schemes. In this paper we derive the outage capacity for several cooperative diversity schemes in decode-and-forward relay networks with a finite number of relay nodes. The obtained expressions are simple and applicable to arbitrary network topologies and signal-to-noise ratios in Rayleigh fading channels. The analysis shows that there exists a signal-to-noise ratio threshold, below which some cooperative diversity schemes are better than direct communication. We propose a new diversity scheme, which, compared to the conventional counterpart, offers improved performance and requires protocol overhead.

Cooperative Multicell ARQ - Packet Error Rate and Throughput Analysis

Future cellular systems such as LTE-Advanced systems offer improved coverage, system throughput, and cell-edge throughput through the effective use of coordinated multi-point processing (CoMP). In this paper, we propose cooperative multicell automatic repeat request (ARQ), which exploits both the cooperation among base stations via backhaul links and ARQ. First, it involves minimal change in the physical-layer and MAC specifications of the mobile to BS connection. Second, spatial diversity is captured with efficient use of bandwidth resource as long as the backhaul links are available. We study three protocols, where BSs cooperate with different multicell processing: opportunistic decode-and-forward, amplify-and-forward, and compress-and-forward. We derive their respective average packet error rates and throughput. The obtained results show that cooperative multicell ARQ protocols are promising in terms of average packet error rate and throughput compared to the conventional ARQ. The parameters that effect the performance of each protocol include the operating SNRs of the main link and backhaul link, the number of neighboring BSs, and the network topology.

On the Design of Space-Frequency Codes from Super-Orthogonal Space-Time Trellis Codes via Mapping

This paper describes how to construct a class of spaces-frequency (SF) codes by mapping the super-orthogonal space-time trellis (SOSTT) codes across OFDM subcarriers. Two mapping methods are employed: conventional repetition mapping and the proposed mapping methods with the design criteria of achieving full diversity including spatial and frequency at the maximum possible transmission rate. The proposed mapping method appears to outperform the conventional mapping counterpart with respect to coding gain when constructing the SF codes mapped from SOSTT codes. Simulation results show the performance gain of 0.5-3 dB under frequency-selective fading channels. In addition, the constructed SF codes mapped with both mapping methods are compared to the existing commonly known SF codes, i.e. the space-time trellis (STT) codes mapped with conventional mapping method. Apparently the SOSTT codes are superior to the STT codes in single-carrier narrowband wireless channel, the mapped SOSTT codes do not offer the same advantage over the mapped STT codes under the severely-frequency-selective fading channel when the codes having large number of states. Nevertheless, some performance improvement is observed for codes with small number of states.

Adaptive Power Allocation for Limited Feedback Multi-Antenna Transmissions

This paper addresses the problem of optimizing the adaptive power allocation for data transmission over wireless communication fading channels using multiple transmit antennas with band-limited feedback channel. The objective of the optimization is to minimize the bit error rate (BER) subject to constraint on the average transmitted power. The chosen multi-antenna transmission scheme is the transmit antenna selection, which requires limited number of feedback bits. The adaptive power allocation is chosen to have finite levels of allocated power so that the system will still require limited number of feedback bits when the proposed adaptive power allocation scheme is combined. The allocated power of each level will be optimally determined. This has to be done with regarding to the employment of antenna selection. In order to achieve this goal, the formula of the BER of the system using transmit antenna selection scheme as a function of allocated power level is first derived. Then, the obtained formula is solved for optimal allocated power of each level. The obtained results shows that the advantageous features of two different techniques, namely antenna selection and the adaptive power allocation, can be combined effectively to combat fading using limited feedback information. Numerical results of the systems with 2-transmit and 3-transmit antenna are used here to demonstrate that substantial BER performance improvement can be achieved by using even only a few power adaptation levels.

Cooperative multicell ARQ in MIMO cellular systems

Coordinated multi-point processing at multiple base stations can improve coverage and throughput for future cellular systems. In this paper, we study the coordinated reception at multiple MIMO base stations by proposing cooperative multi-cell automatic repeat request (ARQ) protocols via wired backhaul links. In particular, we consider three protocols where the cooperative base stations employ different type of multi-cell processing, namely, opportunistic decode-and-forward, amplify-and-forward, and compress-and-forward processing. We derive the average packet error rates for these protocols. Numerical results show the effectiveness of the proposed protocols compared to conventional ARQ protocol. Furthermore, the degree of improvement depends on the type of cooperative multicell ARQ protocols and the operating average signal-to-noise ratio of the main and backhaul links.

Bandwidth efficient full-diversity SF-MTCM

This paper proposes a new space-frequency (SF) code construction scheme that can fully exploit both spatial and frequency diversities while providing great coding advantage and maintaining high bandwidth efficiency for MIMO-OFDM system operating in frequency-selective channels. The proposed SF code construction method is based on a class of trellis codes, where the trellis branches are labeled with the newly devised multidimensional constellation, which is spread across both the parallel transmission from multiple antennas and adjacent subcarriers transmitted from each antenna, and is referred to here as SF-MTCM. The proposed SF-MTCM is compared to both conventional SFBC and SFTC, which achieve full diversity, at the same bandwidth efficiency level. Simulation results clearly show that the SF-MTCM offers greater coding advantage. Moreover, its superiority is maintained even when the time-delay characteristic of the propagation paths between transmit and receive antennas changes variously.

Improved Rate-One Full-Diversity Space-Frequency Block Code Designs

This work proposes improved rate-1 full-diversity space-frequency block code (SFBC) designs that outperform the existing SFBC designs. It is observed that signal mapping for the existing rate-1 full-diversity SFBC designs can be improved. A simple mapping scheme is proposed here that greatly enhances the resulting performance of the SFBC scheme. The performance gains of the proposed codes are mathematically proven and also illustrated via simulation results

A Design of Space-Frequency Trellis Codes with High Rate and Full Diversity

This paper proposes high-rate full-diversity space-frequency trellis code (SFTC) designs for frequency selective fading channels, which achieve the full diversity advantage at the same transmission rate as the existing space-time block code (STBC) designs. The proposed codes are derived based on the concept of concatenated STBC and multiple trellis coded modulation (MTCM) encoder constructions. The existing space-frequency trellis code designs only provided small frequency diversity and coding gain advantages for the case in which the channel delay spread is small. Here, the proposed SFTC codes achieve larger coding gain and frequency diversity advantages than the existing SFTC designs. Simulation results show the proposed designs significantly outperform the existing space-frequency block code designs and the conventional SFTC designs