mohatta2015.pdf
signal processing from power amplifier operation control point of view
signal processing from power amplifier operation control point of view
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PROBLEMS 95<br />
Another aspect of cochannel interference is its cyclostationarity. We saw cyclostationarity<br />
in the formation of the data covariance matrix, which depends on the<br />
path delays of the interfering symbols. Cyclostationarity of cochannel interference<br />
is addressed in [Ree90, Pet91, Gar93]. Suppression of narrowband interference in a<br />
wideband system is discussed in [Mil88, Gel98].<br />
In CDMA systems, early work focused on multiuser detection in the MIMO/cochannel<br />
scenario. The ZF solution for the synchronous CDMA case (referred to as<br />
the decorrelating receiver) is proposed in [Sch79] and developed in [Lup89]. The<br />
MMSE solution can be found in [Mad94].<br />
For the dispersive/asynchronous case, early work focused on the CDMA uplink<br />
(different channel per user/code). Work on ZF LE is found for the asynchronous<br />
case in [Lup90] and for the dispersive case in [Zvo96a, Zvo96b]. The MMSE solution<br />
can be found in [Xie90a]. When the spreading codes of other users are unknown,<br />
code averaging can be applied [Won98, Won99]. Sub-block linear equalization using<br />
a sliding window is described in [Wij92, Rup94, Wij96, Jun97]. Block linear<br />
equalization is examined in [Kle96]. Linear multiuser detection in rapidly varying<br />
channels is addressed in [Say98]. Linear equalization with continuous-time signals<br />
is considered for CDMA in [Mon94, Yoo96].<br />
Later, the dispersive case was considered for the CDMA downlink (same channel<br />
per user/code). Early work in [Bot93] uses a maximum-SINR approach to<br />
despread-level transversal linear equalization to determine the weight solution. ZF<br />
and MMSE block equalization at the chip level are considered in [Kle97]. In remaining<br />
work, transversal equalization is considered at the chip level [Gha98, JarOl,<br />
Fra02, Kra02] and despread level [Gha98, BotOO, TanOO, Fra02, Mud04]. The chip<br />
level solution is formulated in terms of MMSE estimation of the transmitted composite<br />
chip values (summed over all users). The despread level solution is formulated<br />
in terms of ML [BotOO] or MMSE [Gha98, TanOO, Fra02, Mud04] estimation of the<br />
symbol. In [JarOl], ML block equalization is also considered.<br />
Some form of code averaging is considered in all downlink work cited as a way to<br />
simplify receiver design. With code averaging, expressions for the weights involve<br />
infinite sums, which have a closed form expression for certain chip pulse shapes<br />
[Jat04]. Equivalence of MMSE and ML solutions is shown in [Had04].<br />
Group linear equalization has been studied primarily for CDMA systems. In<br />
[Sch96], ZF LE is used to suppress interference from symbols outside the group.<br />
Code averaging can be used in designing the LE in the MIMO/cochannel [Gra03,<br />
Mai05] and dispersive/asynchronous scenarios [BotlOa].<br />
PROBLEMS<br />
The idea<br />
4.1 Consider the Alice and Bob example. Suppose instead that n = — 1 and<br />
r 2 = 4.<br />
a) What is the value of zi and s