Imperfect Channel State Information in Cooperative Relaying Links

Cooperative relay network

The use of diversity in the spatial and temporal dimension to mitigate the effects of fading and therefore to increase the reliability of radio links in wireless networks is a well known technique for systems with co-located antennas (space-time coding).

Recently a new form of realizing spatial diversity has been introduced in [1] called cooperative diversity or user cooperation diversity. The main idea is to use multiple single antenna nodes as a virtual macro antenna array, realizing spatial diversity in a distributed fashion. In such a network several, maybe idle, nodes serve as relays for an active source-destination pair. Relays can be classified as either decode-and-forward (DF) or amplify-and-forward (AF) relays. AF relays, which are considered in this project, only retransmit an amplified version of their received signals. This leads to low-complexity relay transceivers and to lower power consumption since there is no signal processing for decoding procedures. Moreover, AF relays are transparent to adaptive modulation techniques which may be employed by the source. One disadvantage of AF relays is, that they also amplify their own noise.

The achievable performance of such cooperative diversity schemes depends highly on the amount and quality of the channel state information (CSI) which is available at the receiver [2]. The goal of this project is to compare the performance of the different estimation schemes and to investigate their feasibility for cooperative relay networks. As reference scenario serves the in [3] proposed cooperative diversity scheme.

[1] J. N. Laneman, D. N. Tse, and G. W. Wornell, ''Cooperative diversity in wireless networks: Efficient protocols and outage behavior,'' submitted to IEEE Trans. Inform. Theory, 2002.
[2] H. Meyr, M. Moeneclaey, S. A. Fechtel, ''Digital Communication Receivers: Synchronization, Channel Estimation ans Signal Processing,'' Wiley 1998.
[3] I. Hammerstroem, M. Kuhn, and A. Wittneben, ''Cooperative diversity by relay phase rotations in block fading environments,'' in Proc. SPAWC, Lisbon, Portugal, July, 2004.

Type Student project (Semesterarbeit)
Semester Summer 2005
Subject area Wireless relay networks, channel estimation, and cooperative diversity
Type of work 50% Theory, 25% Software, and 25% Simulations
Student Matthias Gwerder
Supervisor Dr. Ingmar Hammerström
Professor Prof. Dr. Armin Wittneben