Coding Scheme For Transmission Research Articles

Performance Analysis of Code Combining Based Cooperative Protocol with Amplified-and-Forward (AF) Relaying

In this letter, we analyze the error performance of a code combining based cooperative diversity protocol. For coded transmission schemes, code-combining can obtain a near optimal low rate code by combining repeated codewords. An analytical method for evaluating the performances of such scheme is presented. We develop a closed form expression for pairwise error probability and tight upper bounds for bit error rate (BER) and frame error rate (FER) under Rayleigh fading environment. The analytical upper bounds are verified with simulation results.

Quadratic forms in normal RVs: theory and applications to OSTBC over hoyt fading channels

In this paper, the statistics of quadratic forms in normal random variables (RVs) are studied and their impact on performance analysis of wireless communication systems is explored. First, a chi-squared series expansion is adopted to represent the probability density function of a quadratic form in normal RVs and novel series truncation error bounds are derived, which are much tighter compared to already known ones. Secondly, it is theoretically shown that when an orthogonal space time block coding (OSTBC) transmission scheme is used, the signal to noise ratio (SNR) at the receiver under various fading conditions can be expressed as a quadratic form in normal RVs. Capitalizing on these results, a thorough error probability and capacity analysis is presented for the performance of OSTBC systems over Nakagami-q (Hoyt) fading channels. For all error probability and capacity performance criteria considered, simple, closed-form truncation error bounds expressions are derived, which avoid the use of infinite sums and complicated functions. The proposed theoretical analysis is validated through extensive Monte Carlo simulations.

Code Combining in Cooperative Communication

It is well known that cooperative transmission among the single antenna wireless nodes and a proper combining at destination can obtain spatial diversity. In this paper, we introduce a new form of combining technique in cooperative communication. For a coded transmission scheme code-combining can obtain a near optimal low rate code by combining repeated codewords. Instead of MRC (maximal ratio combining) based combining of received coded packets from source and relays, we propose a simple code-combining at destination. For same data, rate and power consumption code-combining offers better or similar performance with less complexity than MRC. Moreover using a puncturing technique at the relay we can get a same diversity order as MRC with reduced packet relaying time; equivalently, with higher data rate for over all system. This reduction of transmission time at relay allows us to increase the diversity order by using more than one relay for one source; where each relay forwards a punctured portion of received data. Alternatively, when the relays are not available to improve diversity order, we can use only one relay to cooperate M source nodes where all sources obtain a diversity order of 2 with a higher data rate.

Analytical assessment of multi-user vs. spatial diversity trade-offs with delayed channel state information

In this letter, we explore the combined use of spatial and multi-user diversity in a cellular system where channel state information is subject to delays in the feedback channel. First, we analytically derive the probability and cumulative density functions of the post-scheduling signal-to-noise ratio (SNR) for both a single-input single-output (SISO) and an orthogonal space-time block coding (OSTBC) transmission schemes. Then, we obtain the closed-form expressions of the corresponding average system capacities. By evaluating those expressions, we analytically show that the OSTBC scheme is far less sensitive to delays in the feedback channel

Adaptive Transmitter Optimization in Multiuser Multiantenna Systems: Theoretical Limits, Effect of Delays, and Performance Enhancements

The advances in programmable and reconfigurable radios have rendered feasible transmitter optimization schemes that can greatly improve the performance of multiple-antenna multiuser systems. Reconfigurable radio platforms are particularly suitable for implementation of transmitter optimization at the base station. We consider the downlink of a wireless system with multiple transmit antennas at the base station and a number of mobile terminals (i.e., users) each with a single receive antenna. Under an average transmit power constraint, we consider the maximum achievable sum data rates in the case of (1) zero-forcing (ZF) spatial prefilter, (2) modified zero-forcing (MZF) spatial prefilter, and (3) triangularization spatial prefilter coupled with dirty-paper coding (DPC) transmission scheme. We show that the triangularization with DPC approaches the closed-loop MIMO rates (upper bound) for higher SNRs. Further, the MZF solution performs very well for lower SNRs, while for higher SNRs, the rates for the ZF solution converge to the MZF rates. An important impediment that degrades the performance of such transmitter optimization schemes is the delay in channel state information (CSI). We characterize the fundamental limits of performance in the presence of delayed CSI and then propose performance enhancements using a linear MMSE predictor of the CSI that can be used in conjunction with transmitter optimization in multiple-antenna multiuser systems.