Showing papers by "Murat Uysal published in 2005"

Distributed space-time block coding with imperfect channel estimation

Abstract: In this paper, we derive closed-form expressions for the bit error rate (BER) for a distributed space-time block coded system, considering both perfect and imperfect channel estimation. For the special case of single relay, under the assumption of an appropriate power control, we show that the diversity order of two is obtained, achieving the maximum diversity order. Our analysis also demonstrates the existence of an error floor due to channel estimation errors.

Maximum achievable diversity order for cascaded Rayleigh fading channels

Abstract: In this Letter, we investigate the error rate performance of coherent M-ary phase shift keying (M-PSK) modulation over cascaded Rayleigh fading with receive antenna diversity. Through the derived symbol error rate (SER) expression, we present the maximum diversity order achievable over such channels and demonstrate the performance degredation in comparison to conventional Rayleigh channels.

On the distributed space-time signal design for a large number of relay terminals

Abstract: We study the asymptotic behavior of a cooperative scheme operating in amplify-and-forward (AF) mode when the number of relay terminals tends to infinity. An optimal code design rule is derived through the investigation of a pairwise error probability (PEP) expression. The design rule is based on an Euclidean-distance-type metric including some scaling terms due to different path loss and shadowing effects associated with underlying relay links. Since the design criterion is channel-dependent, it does not allow a practical code design. However, we further demonstrate that "classical" Euclidean distance can be used as a sub-optimal solution for realizing cooperative diversity advantages which we further verify through our simulation study. Our simulation results also indicate that distributed space-time codes based on Euclidean distance yield good results even for a small number of relays.

Performance analysis of imperfect closed-loop power control over Rayleigh fading

Abstract: The performance of closed-loop power control in code division multiple access systems considering several non-ideal conditions such as multiple power control, group delays, channel estimation error, and power control command bit error probability is investigated.