ChaseLow2: Joint Cooperative Diversity and Scheduling

In a centralized wireless access system a scheduler at the access point schedules the medium access of the wireless user nodes. A channel adaptive scheduler incorporates channel (link) state information (CSI) in this decision (Fig. (a)). As the achievable link level throughput depends on the link quality, channel adaptive scheduling may improve the aggregate throughput. Channel adaptive scheduling is particularly efficient in the high mobility regime, because the channel state varies sufficiently within the latency time scale of interest. The potential benefits of including cooperating idle nodes into the communication of active user nodes has started to attract a lot of research interest. Most work to date has focused on cooperative diversity (Fig. (b)). MIMO wireless utilizes multiple antennas at transmit and receive side to increase the link throughput by spatial multiplexing. Unfortunately this approach requires a propagation environment with rich scattering. Very recently the MIMO concept has been extended to cooperative signalling in order to relieve the rich scattering requirement.

In the project ChaseLow2 we will extend the benefits of cooperative diversity, channel adaptive scheduling and spatial multiplexing (MIMO) into a low mobility environment with poor scattering and with heterogeneous nodes. We refer to this approach as joint cooperative diversity and scheduling (Fig. (c)).

As a first indication of the attainable performance Fig. (d) shows the probability of outage of the aggregate (solid) and the per-link throughput (dashed). Parameter of the curves is the number N of source/destination pairs. In this example we assume L=21 relaying nodes.

For reference the round robin scheduler is shown. Note, that due to the quasi-static channel this reference curve also indicates the performance of a reasonably fair channel adaptive scheduler. For all values of N the joint cooperative scheduling and diversity scheme achieves a substantial diversity gain (slope of the cdf curves). Also clearly visible is the improvement of the aggregate throughput by scheduling N > 1 source/destination pairs. The dashed curves show the per-link throughput. Despite the static channel, the greedy scheduler is reasonably fair, as the per-link outage behaviour is not substantially affected by the number of source/destination pairs. Note, that the joint cooperative diversity and scheduling scheme outperforms the round robin scheduler both in per-link throughput and in aggregate throughput.