53,148 research outputs found
DOPPLER CORRECTION FOR DIGITAL MODULATION IN A FADING CHANNEL WITH SINGLE-INPUT SINGLE-OUTPUT
In a high mobility wireless channel, the Doppler effect is compounded and must be corrected by using pilot-aided
symbols. The pilot symbol rate depends on the severity of the Doppler effect. There are existing algorithms such as
differential decision-feedback (D-DF) and double-differential decision-feedback (DD-DF) for single-input single output (SISO) systems to improve channel tap estimation. Such algorithms improve the bit error rate (BER)
performance of pilot symbol aided decision feedback demodulation. In this thesis, the use of minimum mean square
error (MMSE) estimation was implemented to further improve channel tap estimation for the D-DF and DD-DF
algorithms.
BER performance showed significant improvement for higher order modulation schemes. On the other hand,
implementation of the new algorithm on quadrature phase-shift keying (QPSK) showed negligible improvement.
Also, the MMSE algorithm is not very effective for cases with very high Doppler frequency shifts.
Finally, it was observed that the performance improvement due to MMSE estimation decreases as the signal to-noise ratio increases. To counter this, adaptive tolerances, tied to the variance of channel tap estimation, were
found to provide better channel estimation surge detection capabilities. Such implementation dramatically improved
the bit error rate performances for D-DF with the MMSE algorithm but was not effective for the DD-DF algorithm.Military Expert 5, Republic of Singapore Air ForceApproved for public release; distribution is unlimited
Dispensing with Channel Estimation…
In this article, we investigate the feasibility of noncoherent detection schemes in wireless communication systems as a low-complexity alternative to the family of coherent schemes. The noncoherent schemes require no channel knowledge at the receiver for the detection of the received signal, while the coherent schemes require channel inherently complex estimation, which implies that pilot symbols have to be transmitted resulting in a wastage of the available bandwidth as well as the transmission power
Maximum likelihood detection for differential unitary space-time modulation with carrier frequency offset
Can conventional differential unitary space time modulation (DUSTM) be applied when there is an unknown carrier frequency offset (CFO)? This paper answers this question affirmatively and derives the necessary maximum likelihood (ML) detection rule. The asymptotic performance of the proposed ML rule is analyzed, leading to a code design criterion for DUSTM by using the modified diversity product. The resulting proposed decision rule is a new differential modulation scheme in both the temporal and spatial domains. Two sub-optimal multiple-symbol decision rules with improved performance are also proposed. For the efficient implementation of these, we derive a modified bound intersection detector (BID), a generalization of the previously derived optimal BID for the conventional DUSTM. The simulation results show that the proposed differential modulation scheme is more robust against CFO drifting than the existing double temporal differential modulation
ABC: A Simple Explicit Congestion Controller for Wireless Networks
We propose Accel-Brake Control (ABC), a simple and deployable explicit
congestion control protocol for network paths with time-varying wireless links.
ABC routers mark each packet with an "accelerate" or "brake", which causes
senders to slightly increase or decrease their congestion windows. Routers use
this feedback to quickly guide senders towards a desired target rate. ABC
requires no changes to header formats or user devices, but achieves better
performance than XCP. ABC is also incrementally deployable; it operates
correctly when the bottleneck is a non-ABC router, and can coexist with non-ABC
traffic sharing the same bottleneck link. We evaluate ABC using a Wi-Fi
implementation and trace-driven emulation of cellular links. ABC achieves
30-40% higher throughput than Cubic+Codel for similar delays, and 2.2X lower
delays than BBR on a Wi-Fi path. On cellular network paths, ABC achieves 50%
higher throughput than Cubic+Codel
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