Abstract
Q. Zhao and L. Tong
"Signal Processing for Multiaccess Communication Networks"
Signal Processing for Mobile Communications
Handbook, CRC Press, 2004.
In multiaccess wireless networks where a common channel is shared by a
population of users, both the reception capability of
the common wireless channel and the efficiency of the medium access
control (MAC) protocol affect the network
performance. Traditionally, MAC protocols are designed based on a
collision channel model where any concurrent transmissions result in
the destruction of all transmitted packets. Numerous
protocols, such as ALOHA, the tree algorithm,
the first-come first-serve (FCFS) algorithm,
and a class of adaptive schemes,
have been proposed to coordinate the transmissions of all users for
the efficient utilization of the limited channel reception capability.
The advent of sophisticated signal processing techniques has changed the
underlying assumptions made by conventional MAC protocols. In networks
with space-division multiple access or code-division multiple access,
it is possible to receive some or all simultaneously transmitted
packets which, in the conventional channel, would result in a
collision and require retransmissions. In addition to the direct
throughput improvement resulting from the recovery of colliding
packets, the traffic load caused by retransmissions is reduced, which
further decreases the frequency of collision.
While promising improvement in the overall performance of the network,
this multipacket
reception (MPR) capability presents new
challenges to MAC designers. First, the MPR capability enriches the
channel outcome, which makes it more difficult to infer the state of a
user from the feedback information. Second, the MPR capability opens
new options for collision resolution which, in the conventional
collision channel, can be achieved only by splitting of users. To
fully exploit the MPR capability, new MAC protocols need to be
designed.
In this chapter, we
present signal processing
techniques that enable multipacket reception at the physical layer and
examine their impact on the performance and
design of MAC protocols.