Digital Signal Processing Reference
In-Depth Information
pulse-based wideband radio system is well suited for use in point-to-multipoint
networks. For example, a wireless access point can send interleaved informa-
tion destined for multiple clients in a single packet burst. Based on channel
observations, clients can choose their own number and position of window
slots. The signal energy of the slots is combined by the back-end processor
which controls the receive units (Figure 5.10). The next section describes how
the multiple incoming data streams are interleaved into a single, more reliable
output stream.
5.3
ISSR-based diversity combining
In this section, it is explained how several multipath streams originating from
the parallel units of a pulse-based radio receiver are recombined into a single
stream. Even though the system is described with a strong bias towards pulse-
based radio, its applicability is not limited to this specific domain. Any other
wired or wireless system that is more or less compatible with the issr signal
reconstruction system can make advantage of the issr-based diversity combin-
ing method introduced in this section. It is also assumed that the output signal
originating from the parallel receive units is a single-carrier qpsk modulated
signal. In the pulse-based radio system of which the outlines are being drawn
up in the course of this chapter, the issr-based stream combiner should be lo-
calized in the digital back-end of the receiver. This implies that some crucial
signal-preprocessing steps have already been performed autonomously by the
respective receive units themselves. This includes, for example, the maximiza-
tion of the loading factor of the ad-converters using a variable gain amplifier
(vga) and the removal of out-of-band signal components by fixed-frequency
band-select filters. Also, the conversion from rf to baseband - in this particu-
lar case the bandwidth compression of the rf-pulses (p. 93) - is supposed to
be taken care of by the receive units.
Multi-antenna spatial diversity
With the combination technique that is going to be introduced below, it is not
only possible to interlace the multipath symbol streams that are resolved from a
single antenna, but also from two (or more) physically separated antennas.
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At
first sight, it could seem a bit pointless to introduce costly hardware in the form
of additional antennas. After all, remember that one of the motivations behind
the development of pulse-based wideband radio was the excellent multipath
resolvability of this system thanks to the use of short pulses. So there is no
apparent advantage in the reallocation of some of the receive units to another
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Other possibilities are separate wires, virtual antenna beams from a phased-array grid, ...
