1,559 research outputs found
Interference Suppression in WCDMA with Adaptive Thresholding based Decision Feedback Equaliser
WCDMA is considered as one of the 3G wireless standards by 3GPP. Capacity calculation shows that WCDMA systems have more capacity compared to any other multiple access technique such as time division multiple access (TDMA) or frequency division multiple access (FDMA). So it is widely used. Rake receivers are used for the detection of transmitted data in case of WCDMA communication systems due to its resistance to multipath fading. But rake receiver treat multiuser interference (MUI) as AWGN and have limitation in overcoming the effect of multiple access interference (MAI) when the SNR is high. A de-correlating matched filter has been used in this thesis, which eliminates and improves system performance. But the given receiver works well only in the noise free environment. A DFE, compared to linear equaliser, gives better performance at severe ISI condition. The only problem in this equalisation technique is to select the number of symbols that are to be fed back. This thesis gives an idea on multiple symbol selection, based on sparity where an adaptive thresholding algorithm is used that computes the number of symbols to feedback. Simulated results show a significant performance improvement for Regularised Rake receiver along with thresholding in terms of BER compared to a rake receiver, de-correlating rake receiver and regularised rake receiver. The performance of the receiver in different channels is also analysed
Feedback Allocation For OFDMA Systems With Slow Frequency-domain Scheduling
We study the problem of allocating limited feedback resources across multiple
users in an orthogonal-frequency-division-multiple-access downlink system with
slow frequency-domain scheduling. Many flavors of slow frequency-domain
scheduling (e.g., persistent scheduling, semi-persistent scheduling), that
adapt user-sub-band assignments on a slower time-scale, are being considered in
standards such as 3GPP Long-Term Evolution. In this paper, we develop a
feedback allocation algorithm that operates in conjunction with any arbitrary
slow frequency-domain scheduler with the goal of improving the throughput of
the system. Given a user-sub-band assignment chosen by the scheduler, the
feedback allocation algorithm involves solving a weighted sum-rate maximization
at each (slow) scheduling instant. We first develop an optimal
dynamic-programming-based algorithm to solve the feedback allocation problem
with pseudo-polynomial complexity in the number of users and in the total
feedback bit budget. We then propose two approximation algorithms with
complexity further reduced, for scenarios where the problem exhibits additional
structure.Comment: Accepted to IEEE Transactions on Signal Processin
Performance Analysis of Fully Joint Diversity Combining, Adaptive Modulation, and Power Control Schemes
Adaptive modulation and diversity combining represent very important adaptive
solutions for future generations of wireless communication systems. Indeed, to
improve the performance and the efficiency of these systems, these two techniques
recently have been used jointly in new schemes named joint adaptive modulation
and diversity combining (JAMDC) schemes. Considering the problem of finding lowcomplexity,
bandwidth-efficient, and processing-power efficient transmission schemes
for a downlink scenario and capitalizing on some of these recently proposed JAMDC
schemes, we propose and analyze three fully joint adaptive modulation, diversity
combining, and power control (FJAMDC) schemes. More specifically, the modulation
constellation size, the number of combined diversity paths, and the needed power
level are determined jointly to achieve the highest spectral efficiency with the lowest
possible combining complexity, given the fading channel conditions and the required
bit error rate (BER) performance. The performance of these three FJAMDC schemes
is analyzed in terms of their spectral efficiency, processing power consumption, and
error-rate performance. Selected numerical examples show that these schemes considerably
increase the spectral efficiency of the existing JAMDC schemes with a slight increase in the average number of combined paths for the low signal to noise ratio
range while maintaining compliance with the BER performance and a low radiated
power resulting in a substantial decrease in interference to co-existing systems/users
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