226 research outputs found
Maximum likelihood detection for decode and forward cooperation with interference
In this paper, we obtain the maximum likelihood (ML) decision for a decode and forward (DF) cooperative system in Nakagami-m fading in the presence of co-channel interference at the relay as well as the destination. Through simulation results, we first show that conventional ML designed for interference free systems fails to combat the deleterious effect of interference. An optimum ML decision for combating interference is then derived for integer m. This receiver is shown to be superior to conventional ML through bit error rate (BER) performance simulations. Further, our results also indicate that optimum ML preserves relay diversity in the presence of interference
Performance analysis of diversity techniques in wireless communication systems: Cooperative systems with CCI and MIMO-OFDM systems
This Dissertation analyzes the performance of ecient digital commu- nication systems, the performance analysis includes the bit error rate (BER) of dier- ent binary and M-ary modulation schemes, and the average channel capacity (ACC) under dierent adaptive transmission protocols, namely, the simultaneous power and rate adaptation protocol (OPRA), the optimal rate with xed power protocol (ORA), the channel inversion with xed rate protocol (CIFR), and the truncated channel in- version with xed transmit power protocol (CTIFR). In this dissertation, BER and ACC performance of interference-limited dual-hop decode-and-forward (DF) relay- ing cooperative systems with co-channel interference (CCI) at both the relay and destination nodes is analyzed in small-scale multipath Nakagami-m fading channels with arbitrary (integer as well as non-integer) values of m. This channel condition is assumed for both the desired signal as well as co-channel interfering signals. In addition, the practical case of unequal average fading powers between the two hops is assumed in the analysis. The analysis assumes an arbitrary number of indepen- dent and non-identically distributed (i.n.i.d.) interfering signals at both relay (R) and destination (D) nodes. Also, the work extended to the case when the receiver employs the maximum ratio combining (MRC) and the equal gain combining (EGC) schemes to exploit the diversity gain
Outage Probability Analysis of Dual Hop Relay Networks in Presence of Interference
Cooperative relaying improves the performance of wireless networks by forming a network of multiple independent virtual sources transmitting the same information as the source node. However, interference induced in the network reduces the performance of cooperative communications. In this work the statistical properties, the cumulative distribution function (CDF) and the probability density function (PDF) for a basic dual hop cooperative relay network with an arbitrary number of interferers over Rayleigh fading channels are derived. Two system models are considered: in the first system model, the interferers are only at the relay node; and in the second system model, interferers are both at the relay and the destination. This work is further extended to Nakagami-m faded interfering channels. Simulation results are presented on outage probability performance to verify the theoretical analysis
Cooperative Diversity in CDMA over Nakagami−m Fading Channels
Spatial diversity can be employed by sending copies of the transmitted signal using
multiple antennas at the transmitter/receiver, as implemented in multiple-input multipleoutput
(MIMO) systems. Spatial receive diversity has already been used in many applications
with centralized systems where base station receivers are equipped with multiple
antennas. However, due to the power constraints and the small size of the mobile terminal,
it may not be feasible to deploy multiple transmit antennas. User cooperation
diversity, a new form of space diversity, has been developed to address these limitations.
Recently, user cooperative diversity has gained more attention as a less complex alternative
to centralized MIMO wireless systems. It revealed the ability to improve wireless
communications through reliable reception.
One common network of the user cooperation diversity is the direct sequence code
division multiple access (DS-CDMA) in which the Rayleigh fading channels are adopted
and the orthogonality between users is assumed. The Rayleigh fading channels are unrealistic
since they cannot represent the statistical characteristics of the complex indoor
environments. On the other hand, Nakagami-m fading model is well known as a generalized
distribution, where many fading environments can be modeled. It can be used to
model fading conditions ranging from severe, light to no fading, by changing its fading parameter m.
The bit-error-rate (BER) and outage probability of uplink cooperative DS-CDMA over
Nakagami-m has not been addressed in the literature. Thus, in this thesis, the performance
of both decode-and-forward (DF) and amplify-and-forward (AF) cooperative
asynchronous DS-CDMA system over Nakagami-m fading channels is investigated. The
Rake receiver is used to exploit the advantages of multipath propagation. Besides, multiuser
detection (MUD) is used to mitigate the effect of multiple-access interference (MAI).
We show that our proposed multi-user system achieves the full system diversity gain.
The first part of the thesis introduces a new closed-form expression for the outage
probability and the error probability of the DF cooperative DS-CDMA over asynchronous
transmission over independent non-identical Nakagami-m fading channels. The underlying
system employs MUD such as minimum mean square error (MMSE) and decorrelator
detector (DD) to achieve the full diversity. The aforementioned closed-form expression
is obtained through the moment generating function (MGF) for the total signal-to-noise
ratio (SNR) at the base station where the cumulative density function (CDF) is obtained.
Furthermore, we investigate the asymptotic behavior of the system at high SNR to calculate
the achievable diversity gain. The results demonstrate that the system diversity gain
is fulfilled when MUD is used to mitigate the effect of MAI.
In the second part of the thesis, we study the performance of cooperative CDMA
system using AF relaying over independent non-identical distribution (i.n.i) Nakagami-m
fading channels. Using the MGF of the total SNR at the base station, we derive the outage
probability of the system. This enables us to derive the asymptotic outage probability for
any arbitrary value of the fading parameter m.
The last part of the thesis investigates the optimum power allocation and optimum
relay location in AF cooperative CDMA systems over i.n.i Nakagami-m fading channels.
Moreover, we introduce the joint optimization of both power allocation and relay location
under the transmit power constraint to minimize the outage probability of the system.
The joint optimization of both power allocation and relay location is used to minimize
the outage performance of the system, thereby achieving full diversity gain
Performance study of an underlay cognitive radio network in the presence of co-channel interference
PhD ThesisMassive innovation in all aspects of the wireless communication network
has been witnessed over the last few decades. The demand for data
throughput is continuously growing, as such, the current regulations for
allocating frequency spectrum are not able to respond to this exponential growth. Cognitive radio (CR), has been proposed as a solution to
this problem. One of the possible scenarios of the implementation of CR
is underlay cognitive radio. In this thesis the performance of an underlay cognitive radio network (UCRN) in the presence of the co-channel
interference (CCI) is assessed.
Firstly, the impact of CCI on the dual-hop cooperative UCRN is investigated over Rayleigh fading channels. In order to do this, the exact outage
probability (OP), average error probability (AEP) and the ergodic capacity (EC) are studied. In addition, simple and asymptotic expressions
for the OP and AEP are derived. Furthermore, the optimal power allocation is investigated to enhance the network performance. Moreover,
the performance of a multi-user scenario is studied by considering the
opportunistic SNR-based selection technique.
Secondly, the effect of both primary network interference and CCI on
the dual-hop UCRN over Rayleigh fading channels are studied. The
equivalent signal-to-interference-plus-noise ratio (SINR) for this network
scenario is obtained by considering multi-antenna schemes at all receiver
nodes. The different signal combinations at the receiver nodes are investigated and compared, such as selection combining (SC) and maximum
ratio combining (MRC) techniques. Then, the equivalent probability
density function (PDF) and cumulative distribution function (CDF) of
the network’s equivalent SINR are derived and discussed. Furthermore,
expressions for the exact OP, AEP, and EC are derived and reviewed.
In addition, asymptotic OP expressions are obtained for different case
scenarios to gain an insight into the network parameters.
Thirdly, multiple-input multiple-output (MIMO) UCRN is investigated
under the influence of primary transmitter interference and CCI over
Rayleigh fading channels. The transmit antenna selection and maximum
ratio combining (TAS/MRC) techniques are considered for examining
the performance of the secondary network. At first the equivalent SINR
for the system is derived, then the exact and approximate expressions
for the OP are derived and discussed.
Fourthly, considering Nakagami-m fading channels, the performance of
the UCRN is thoroughly studied with the consideration of the impact
of primary network interference and CCI. The equivalent SINR for the
secondary system is derived. Then, the system equivalent PDF and CDF
are derived and discussed. Furthermore, the OP and AEP performances
are investigated.
Finally, for the cases mentioned above, numerical examples in conjunction with MatLab Monte Carlo simulations are provided to validate the
derived results. The results show that CCI is one of the factors that
severely reduces the UCRN performance. This can be more observable
when the CCI power increases linearly with the transmission power of
the secondary transmitter nodes. Furthermore, it was found that in
a multi-user scenario the opportunistic SNR-based selection technique
consideration can improve the performance of the network. Moreover,
adaptive power allocation is found to give better results than equal power
allocation. In addition, cooperative communication can be considered to
be an effective way to combat the impact of transmission power limitation of the secondary network and interference power constraint. The
multi-antenna schemes are another important consideration for enhancing the overall performance. In fact, despite the interference from the
CCI and primary user sources, the multi-antennas scheme does not lose
its advantage in the UCRN performance improvementHigher Committee for Education Development in Iraq (HCED). I am also grateful to
the Ministry of Transportation and Communication, Kurdistan Regional
Government-Iraq
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