3,059 research outputs found
Characterization of Coded Random Access with Compressive Sensing based Multi-User Detection
The emergence of Machine-to-Machine (M2M) communication requires new Medium
Access Control (MAC) schemes and physical (PHY) layer concepts to support a
massive number of access requests. The concept of coded random access,
introduced recently, greatly outperforms other random access methods and is
inherently capable to take advantage of the capture effect from the PHY layer.
Furthermore, at the PHY layer, compressive sensing based multi-user detection
(CS-MUD) is a novel technique that exploits sparsity in multi-user detection to
achieve a joint activity and data detection. In this paper, we combine coded
random access with CS-MUD on the PHY layer and show very promising results for
the resulting protocol.Comment: Submitted to Globecom 201
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
On the Performance Gain of NOMA over OMA in Uplink Communication Systems
In this paper, we investigate and reveal the ergodic sum-rate gain (ESG) of
non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in
uplink cellular communication systems. A base station equipped with a
single-antenna, with multiple antennas, and with massive antenna arrays is
considered both in single-cell and multi-cell deployments. In particular, in
single-antenna systems, we identify two types of gains brought about by NOMA:
1) a large-scale near-far gain arising from the distance discrepancy between
the base station and users; 2) a small-scale fading gain originating from the
multipath channel fading. Furthermore, we reveal that the large-scale near-far
gain increases with the normalized cell size, while the small-scale fading gain
is a constant, given by = 0.57721 nat/s/Hz, in Rayleigh fading
channels. When extending single-antenna NOMA to -antenna NOMA, we prove that
both the large-scale near-far gain and small-scale fading gain achieved by
single-antenna NOMA can be increased by a factor of for a large number of
users. Moreover, given a massive antenna array at the base station and
considering a fixed ratio between the number of antennas, , and the number
of users, , the ESG of NOMA over OMA increases linearly with both and
. We then further extend the analysis to a multi-cell scenario. Compared to
the single-cell case, the ESG in multi-cell systems degrades as NOMA faces more
severe inter-cell interference due to the non-orthogonal transmissions.
Besides, we unveil that a large cell size is always beneficial to the ergodic
sum-rate performance of NOMA in both single-cell and multi-cell systems.
Numerical results verify the accuracy of the analytical results derived and
confirm the insights revealed about the ESG of NOMA over OMA in different
scenarios.Comment: 51 pages, 7 figures, invited paper, submitted to IEEE Transactions on
Communication
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