Massive multiple-input-multiple-output (MM) is becoming a promising candidate for wireless
communications. The idea behind MM is to use a very large number of antennas to increase
throughput and energy efficiency by one or more orders of magnitude. In order to make MM
feasible, many challenges remain. In the uplink a fundamental question is whether to deploy
single massive arrays or to build a virtual array using cooperative base stations. Also, in such
large arrays the signal processing involved in receiver combining is non-trivial. Therefore, low
complexity receiver designs and deployment scenarios are essential aspects of MM and the
thesis mainly focuses on these two areas.
In the first part, we investigate three deployment scenarios: (i) a massive co-located array
at the cell center; (ii) a massive array clustered at B discrete locations; and (iii) a massive
distributed array with a uniform distribution of individual antennae. We also study the effect of
propagation parameters, system size, correlation and channel estimation error. We demonstrate
by analysis and simulation that in the absence of any system imperfections, a massive distributed
array is preferable. However, an intermediate deployment such as a massive array clustered at a
few discrete locations can be more practical to implement and more robust to imperfect channel
state information. We then focus on the performance of the co-located scenario with different
types of antenna array, uniform square and linear arrays. With MM, it may be the case that
large numbers of antennas are closely packed to fit in some available space. Hence, channel
correlations become important and therefore we investigate the space requirements of different
array shapes. In particular, we evaluate the system performance of uniform square and linear
arrays by using ergodic capacity and capacity outage. For a range of correlation models, we
demonstrate that the uniform square array can yield similar performance to a uniform linear
array while providing considerable space saving.
In the second part of the thesis we focus on low complexity receiver designs. Due to the high dimension of MM systems there is a considerable interest in detection schemes with a
better complexity-performance trade-off. We focus on linear receivers (zero forcing (ZF) and
maximum ratio combining (MRC)) used in conjuction with a Vertical Bell Laboratories Layered
Space Time (V-BLAST) structure. Our first results show that the performance of MRC
V-BLAST approaches that of ZF V-BLAST under a range of imperfect CSI levels, different
channel powers and different types of arrays as long as the channel correlations are not too
high. Subsequently, we propose novel low complexity receiver designs which maintain the
same performance as ZF or ZF V-BLAST. We show that the performance loss of MRC relative
to ZF can be removed in certain situations through the use of V-BLAST. The low complexity
ordering scheme based on the channel norm (C-V-BLAST) results in a V-BLAST scheme with
MRC that has much less complexity than a single ZF linear combiner. An analysis of the SINR
at each stage of the V-BLAST approach is also given to support the findings of the proposed
technique. We also show that C-V-BLAST remains similar to ZF for more complex adaptive
modulation systems and in the presence of channel estimation error, C-V-BLAST can be superior.
These results are analytically justified and we derive an exhaustive search algorithm for
power control (PC) to bound the potential gains of PC. Using this bound, we demonstrate that
C-V-BLAST performs well without the need for additional PC. The final simplification is based
on the idea of ordering users based on large scale fading information rather than instantaneous
channel knowledge for a V-BLAST scheme with MRC (P-V-BLAST). An explicit closed form
analysis for error probability for both co-located and distributed BSs is provided along with a
number of novel performance metrics which are useful in designing MM systems. It is shown
that the error performance of the distributed scenario can be well approximated by a modified
version of a co-located scenario. Another potential advantage of P-V-BLAST is that the ordering
can be obtained as soon as the link gains are available. Hence, it is possible that mean
SINR values could be used for scheduling and other link control functions. These mean values are solely functions of the link gains and hence, scheduling, power adaptation, rate adaptation,
etc. can all be performed more rapidly with P-V-BLAST. Hence, the P-V-BLAST structure may
have further advantages beyond a lower complexity compared to C-V-BLAST.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/10517 |
| Date | January 2015 |
| Creators | Alnajjar, Khawla |
| Publisher | University of Canterbury. Electrical and Computer Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Khawla Alnajjar, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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