Reconfigurable Baseband Processing for Wireless Communications - Adaptive Signal Processing in Wireless Communications - page 449

allowed) latency. The reason is that the GT traffic utilizes the bandwidth unused by the
BE traffic. The latency of the GT packets is higher than the latency of the BE traffic
because the GT packets are larger (256 bytes compared with 10 bytes for BE packets).
With the increase of the BE load, the latency of the GT traffic increases too until the
maximum delay reaches the limit. Further increase of the BE load increases the GT
mean latency, but the GT maximum latency never exceeds the guaranteed latency.
Combining guaranteed traffic with best-effort traffic is hard [42]. When using dedi-
cated techniques for both types of traffic, it is possible to reduce the total area and
power consumption. The reasons for reconsidering circuit switching are that the flex-
ibility of packet switching is not needed because a connection between two tiles will
remain open for a long period (e.g., seconds or longer). Furthermore, large amounts of
the traffic between tiles will need guaranteed throughput, which is easier to satisfy in a
circuit-switched connection. Circuit switching also eases the implementation of asyn-
chronous communication techniques, because data and control can be separated and
circuit switching has a minimal amount of control in the data path (e.g., no arbitration).
This increases the energy efficiency per transported bit and the maximum throughput.
Further, scheduling communication streams over non-time-multiplexed channels is
easier because, by definition, a stream will not have collisions with other communica-
tion streams. In contrast with this, the Æthereal [23] routers are using time-multiplexed
channels, and therefore have large interaction between data streams and have to guar-
antee contention free paths. Determining the static time slots table for these systems
requires considerable effort. Because data streams are physically separated in a cir-
cuit-switched NoC, collisions do not occur. Therefore, no buffering and arbitration is
required in the individual router. An example of a circuit-switched NoC is described in
[51]. The number of parallel physical channels between routers is increased to increase
the amount of simultaneously active circuitries. This solution utilizes the huge amount
of wire resources provided by current and future silicon technologies.

15.3 Applications

In this section, we will discuss the mapping onto a heterogeneous SoC of different
licensed communication standards and the mapping of the emerging cognitive radio
application. Concerning licensed communication standards, first the realization of a
UMTS receiver is given. Next, realizations of an OFDM receiver are presented. Finally,
several digital broadcasting systems are discussed.

15.3.1 Licensed Communications

15.3.1.1 UMTS Receiver on Reconfigurable Hardware
The Universal Mobile Telecommunications System (UMTS) standard, defined by
European Telecommunication Standards Institute (ETSI) [2], is an example of a third-
generation (3G) mobile communication system. The communication system has an air
interface that is based on direct-sequence code division multiple access (DS-CDMA)