40 research outputs found
무μ μ€κ³ λ€νΈμν¬μμ μ νΈλμ‘μλΉμ λμ λΆν¬ν¨μ κΈ°λ° μ€κ³κΈ° μ ν κΈ°λ²μ μ±λ₯ λΆμ
νμλ
Όλ¬Έ (λ°μ¬)-- μμΈλνκ΅ λνμ : μ κΈ°Β·μ»΄ν¨ν°κ³΅νλΆ, 2015. 8. μ΄μ¬ν.무μ μ€κ³ κΈ°μ μ μ°¨μΈλ 무μ ν΅μ μμ€ν
μμ μꡬλλ λμ μλΉμ€ νμ§ λ° λ°μ΄ν° μ μ‘λ₯ λ¬μ±μ μν΄ κ³ λ €λκ³ μλ λνμ μΈ κΈ°μ μ€ νλμ΄λ€. 무μ μ€κ³ κΈ°μ μ΄ κ°κ³ μλ λ€μν μ₯μ μΌλ‘ μΈν΄ νμ¬κΉμ§ IEEE 802.16j λ° 3GPP LTE-Advanced λ±μ 무μ ν΅μ μμ€ν
νμ€μ λ°μλκΈ°λ νμλ€.
μ€μ§μ μΌλ‘ λ λ
Έλ μ¬μ΄ μ±λμ ν΅κ³μ νΉμ±μ κ·Έλ€μ μμΉμ λ°λΌ λ¬λΌμ§κΈ° λλ¬Έμ κ° μ±λλ€μ ν΅κ³μ νΉμ±μ μλ‘ λμΌνμ§ μλ€. κ° μ±λλ€μ ν΅κ³μ νΉμ±μ΄ λμΌνμ§ μμ λ, 무μ μ€κ³ κΈ°μ μμ κ°μ₯ μ μ©ν κΈ°λ² μ€ νλμΈ μ€κ³κΈ° μ ν κΈ°λ²μ νΉμ μ€κ³κΈ°λ€μ΄ λ μμ£Ό μ νλλ λ±μ 곡μ μ± λ¬Έμ λ₯Ό μ λ°μν¬ μ μλ€. νΉν, μ΄ λ¬Έμ λ μ νλ λ°°ν°λ¦¬λ₯Ό κ°μ§ μ€κ³κΈ°λ€λ‘ ꡬμ±λ λ€νΈμν¬μμ λ€νΈμν¬μ μλͺ
μ μ€μ΄κ² νλ μμΈμ΄ λ μ μλ€. λ°λΌμ μ΄λ¬ν λ€νΈμν¬μμλ μ¬μ©μλ€μ ν΅μ μ λ’°λ λΏλ§ μλλΌ, μ€κ³κΈ°μμμ μ ν 곡μ μ±λ ν¨κ» κ³ λ €ν νμκ° μλ€.
λ³Έ λ
Όλ¬Έμμλ 무μ μ€κ³ λ€νΈμν¬μμ μ¬μ©μλ€μ ν΅μ μ λ’°λμ μ€κ³κΈ° κ°μ μ ν 곡μ μ±μ ν¨κ» κ³ λ €νκΈ° μν΄ μμ μ νΈλμ‘μλΉμ λμ λΆν¬ν¨μλ₯Ό κΈ°λ°μΌλ‘ νλ μλ‘μ΄ μ€κ³κΈ° μ ν κΈ°λ²μ μ μνλ€. μ£Όμν μ°κ΅¬ κ²°κ³Όλ λ€μκ³Ό κ°λ€.
λ¨Όμ , λμΉ΄κ°λ―Έ-m νμ΄λ© μ±λ νκ²½μ κ°μ§ μΌλ°©ν₯ μ€κ³ λ€νΈμν¬λ₯Ό μν νλ‘μ‘ν°λΈ(proactive) λ° λ¦¬μ‘ν°λΈ(reactive) λ°©μμ μμ μ νΈλμ‘μλΉ λμ λΆν¬ν¨μ κΈ°λ° μ€κ³κΈ° μ ν κΈ°λ²μ μ μνλ€. κ°κ°μ μ€κ³κΈ° μ ν κΈ°λ²μ μν΄ μ€κ³κΈ° μ ν νλ₯ μ μ λνμ¬ μ μλ κ° μ€κ³κΈ° μ ν κΈ°λ²λ€μ νκ· μ€κ³κΈ° 곡μ μ±μ λΆμνλ€. λν κ° μ ν κΈ°λ²μ λν λΆλ₯ νλ₯ μ μμμΌλ‘ μ λνκ³ , μ λν λΆλ₯ νλ₯ μ μ κ·Όμ ννμΌλ‘ λνλ΄μ΄ κ° κΈ°λ²λ€μ΄ μ»μ μ μλ λ€μ΄λ²μν° μ°¨μλ₯Ό λΆμνλ€. λͺ¨μμ€νμ ν΅ν΄ μ»μ΄μ§ νκ· μ€κ³κΈ° 곡μ μ±κ³Ό λΆλ₯ νλ₯ μ΄ μ λν νκ· μ€κ³κΈ° 곡μ μ± λ° λΆλ₯ νλ₯ κ°κ³Ό μΌμΉν¨μ νμΈνλ€. κ·Έλ¦¬κ³ μ μλ κΈ°λ²μ΄ μ€κ³κΈ°λ€ μ¬μ΄μ 곡μ μ±μ μλ²½νκ² λ³΄μ₯νκ³ λ€νΈμν¬ μλͺ
μ μ¦κ°μν€λ©°, λ€μ΄λ²μν° μ°¨μκ° μ€κ³κΈ°μ μμ νμ΄λ© νλΌλ―Έν° m κ°μ λ°λΌ λ¬λΌμ§μ νμΈνλ€.
λμ§Έ, λμΉ΄κ°λ―Έ-m νμ΄λ© μ±λ νκ²½μ κ°μ§ μλ°©ν₯ μ€κ³ λ€νΈμν¬λ₯Ό μν νλ‘μ‘ν°λΈ λ° λ¦¬μ‘ν°λΈ λ°©μμ μμ μ νΈλμ‘μλΉ λμ λΆν¬ν¨μ κΈ°λ° μ€κ³κΈ° μ ν κΈ°λ²μ μ μνλ€. μ μλ νλ‘μ‘ν°λΈ λ°©μμ μ€κ³κΈ° μ ν κΈ°λ²μ λν΄μλ μ νν μ€κ³κΈ° μ ν νλ₯ μ μ λλ₯Ό ν΅ν΄ νκ· μ€κ³κΈ° 곡μ μ±μ λΆμνλ€. μ μλ 리μ‘ν°λΈ λ°©μμ μ€κ³κΈ° μ ν κΈ°λ²μ λν΄μλ μ€κ³κΈ° μ ν νλ₯ μ μ λΆ λ° κ·Όμ¬ ννμ μ λνμ¬ νκ· μ€κ³κΈ° 곡μ μ±μ λΆμνλ€. λν κ° μ ν κΈ°λ²μ λν λΆλ₯ νλ₯ μ μμμΌλ‘ μ λνκ³ , μ λν λΆλ₯ νλ₯ μ μ κ·Όμ ννμΌλ‘ λνλ΄μ΄ κ° κΈ°λ²λ€μ΄ μ»μ μ μλ λ€μ΄λ²μν° μ°¨μλ₯Ό λΆμνλ€. λͺ¨μμ€νμ ν΅ν΄ μ»μ΄μ§ νκ· μ€κ³κΈ° 곡μ μ±κ³Ό λΆλ₯ νλ₯ μ΄ μ λν νκ· μ€κ³κΈ° 곡μ μ± λ° λΆλ₯ νλ₯ κ°κ³Ό μΌμΉν¨μ νμΈνλ€. κ·Έλ¦¬κ³ μ μλ κΈ°λ²μ΄ μ€κ³κΈ°λ€ μ¬μ΄μ 곡μ μ±μ μλ²½νκ² λ³΄μ₯νκ³ λ€νΈμν¬ μλͺ
μ μ¦κ°μν€λ©°, λ€μ΄λ²μν° μ°¨μκ° μ€κ³κΈ°μ μμ νμ΄λ© νλΌλ―Έν° m κ°μ λ°λΌ λ¬λΌμ§μ νμΈνλ€.Wireless relay technology is one of the most promising technologies for the future communication systems which provide coverage extension and better quality of service (QoS) such as higher data rate and lower outage probability with few excessive network loads. Due to its advantages, it has been adopted in wireless standards such as IEEE 802.16j and 3GPP LTE-Advanced.
In practice, since statistics of the channel between any two nodes vary depending on their locations, they are not identical which means that channels can experience different fading. When statistics of the channel are not identical, relay selection, which is one of the most useful techniques for wireless relay technology, can cause fairness
problem that particular relays are selected more frequently than other relays. Especially, this problem can cause reduction of lifetime in the network with multiple relays having limited battery power. In this network, it is needed to focus on selection fairness for relays as well as reliability at end-users.
In this dissertation, to focus on both selection fairness for relays and reliability at end-users, we propose novel relay selection schemes based on cumulative distribution functions (CDFs) of signal-to-noise ratios (SNRs) in wireless relay networks. The dissertation consists of two main results.
First, we propose the proactive and the reactive relay selection schemes based on CDFs of SNRs for one-way relay networks over Nakagami-m fading channels. If a relay
is selected before the source transmission, it is called as proactive relay selection. Otherwise, if a relay is selected after the source transmission, it is called as reactive relay selection. For both the proactive and the reactive relay selection schemes, we analyze average relay fairness by deriving relay selection probability. For the proactive
relay selection scheme, we obtain diversity order by deriving the integral and asymptotic expressions for outage probability. Also, for the reactive relay selection scheme, we obtain diversity order by deriving the exact closed-form and asymptotic expressions for outage probability. Numerical results show that the analytical results of the proposed schemes match the simulation results well. It is shown that the proposed schemes guarantee strict fairness among relays and extend network lifetime. Also, it is shown that diversity order depends on the number of relays and fading severity parameters.
Second, we propose the proactive and the reactive relay selection schemes based on CDFs of SNRs for two-way relay networks over Nakagami-m fading channels. For
the proactive relay selection scheme, we analyze average relay fairness by deriving relay selection probability. Also, we analyze diversity order by deriving the integral and asymptotic expressions for outage probability. For the reactive relay selection scheme, we analyze average relay fairness by deriving the integral and asymptotic expressions for relay selection probability. Also, we obtain diversity order by deriving the asymptotic expression for outage probability. Numerical results show that the analytical results of the proposed schemes match the simulation results well. It is shown that the proposed schemes guarantee strict fairness among relays and extend network lifetime. Also, it is shown that diversity order depends on the number of relays and fading severity parameters.Contents
Abstract i
1 Introduction 1
1.1 Background and Related Work . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 Wireless Relay Technology . . . . . . . . . . . . . . . . . . . . 3
1.2 Outline of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Notations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Relay Selection Based on CDFs of SNRs for One-Way Relay Networks
14
2.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.1 Proactive CDF-Based Relay Selection . . . . . . . . . . . . . 19
2.1.2 Reactive CDF-Based Relay Selection . . . . . . . . . . . . . . 20
2.2 Performance Analysis of Proactive CDF-Based Relay Selection . . . . 22
2.2.1 Average Relay Fairness Analysis . . . . . . . . . . . . . . . . . 22
2.2.2 Outage Probability Analysis . . . . . . . . . . . . . . . . . . . 27
2.3 Performance Analysis of Reactive CDF-Based Relay Selection . . . . 34
2.3.1 Average Relay Fairness Analysis . . . . . . . . . . . . . . . . . 34
2.3.2 Outage Probability Analysis . . . . . . . . . . . . . . . . . . . 36
2.4 Numerical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.4.1 Average Relay Fairness . . . . . . . . . . . . . . . . . . . . . . 39
2.4.2 Network Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.4.3 Outage Probability . . . . . . . . . . . . . . . . . . . . . . . . 53
2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3 Relay Selection Based on CDFs of SNRs for Two-Way Relay Networks
66
3.1 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.1.1 Proactive CDF-based Relay Selection . . . . . . . . . . . . . . 68
3.1.2 Reactive CDF-based Relay Selection . . . . . . . . . . . . . . 72
3.2 Performance Analysis of Proactive CDF-Based Relay Selection . . . . 73
3.2.1 Average Relay Fairness Analysis . . . . . . . . . . . . . . . . . 73
3.2.2 Outage Probability Analysis . . . . . . . . . . . . . . . . . . . 74
3.3 Performance Analysis of Reactive CDF-Based Relay Selection . . . . 82
3.3.1 Average Relay Fairness Anlaysis . . . . . . . . . . . . . . . . . 82
3.3.2 Outage Probability Analysis . . . . . . . . . . . . . . . . . . . 86
3.4 Numerical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.4.1 Average Relay Fairness . . . . . . . . . . . . . . . . . . . . . . 89
3.4.2 Network Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . 100
3.4.3 Outage Probability . . . . . . . . . . . . . . . . . . . . . . . . 105
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4 Conclusion 116
4.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
4.2 Possible Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.2.1 Device-to-Device (D2D) Communications . . . . . . . . . . . 118
4.2.2 Low Power Body Sensor Networks . . . . . . . . . . . . . . . 120
4.3 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Bibliography 122
Korean Abstract 139Docto
Cooperative Diversity in CDMA over Nakagamiβm 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