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Figure 2: Bit error rate performance for cooperative diver- sity transmission in a symmetric network

Figure 2 Bit error rate performance for cooperative diver- sity transmission in a symmetric network

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Figure 1: Cooperative diversity transmission for a 2-user CDMA system In order to facilitate our presentation, we begin with M = 2 and generalize to any M in later sections. Coop- erative transmission with 2 users in a DS-CDMA system is shown in Fig.1.
Figure 1: Cooperative diversity transmission for a 2-user CDMA system In order to facilitate our presentation, we begin with M = 2 and generalize to any M in later sections. Coop- erative transmission with 2 users in a DS-CDMA system is shown in Fig.1.
We assume that the channel between transmitting termi- nals (inter-user channel) and each terminal to the BS (for- ward channels or uplinks) are mutually independent in a cooperative transmission system. The fading amplitude is reciprocal, for instance, hj,2 = ho,1, given U; and U2 co- operating with each other. Additionally, receivers have pre- cise channel state information of the appropriate fading pro- cesses but the transmitters do not exploit such information.
We assume that the channel between transmitting termi- nals (inter-user channel) and each terminal to the BS (for- ward channels or uplinks) are mutually independent in a cooperative transmission system. The fading amplitude is reciprocal, for instance, hj,2 = ho,1, given U; and U2 co- operating with each other. Additionally, receivers have pre- cise channel state information of the appropriate fading pro- cesses but the transmitters do not exploit such information.
Figure 3: An example infrastructure network with 10 mo- bile nodes Next we consider applying cooperative diversity in a centralized network consisting of AK nodes. The CDMA network has a uniform stationary distribution over a unit square area, with infrastructure node (BS) located at the ori- gin of the area. An example network with I” = 10 is shown in Fig.3, where Vi; denotes the BS.
Figure 3: An example infrastructure network with 10 mo- bile nodes Next we consider applying cooperative diversity in a centralized network consisting of AK nodes. The CDMA network has a uniform stationary distribution over a unit square area, with infrastructure node (BS) located at the ori- gin of the area. An example network with I” = 10 is shown in Fig.3, where Vi; denotes the BS.
Coo peration pairs are picked up from the network inde- pendently on their locations. The set Sy contains all oddly indexed nodes and set Sp contains all evenly indexed nodes. U, coo perates with Uj;,+1 if k is aodd number. Fig.4 shows the average bit error rate versus the number of mobile users K, with identical crosscorrelation p = 1/31. In order to exploit the additional diversity gain from user cooperation, it is important to ensure a relative low average BER at re- lay nod es, such that they can reliably detect their sources and forward the information bits. On the contrary, if the inter-user channel quality is very poor, the benefit from co- operation is limited. For comparison, we present the per- formance with either a MMSE detector or a matched filter being used at relay nodes, and MMSE detector at the base station. We observe that the average BER is robust to the number of users if MMSE detection is adopted at each re- lay. However, in the case of matched filter, MAI caused by non-orthogonal spreading codes adversely affects the av- erage BER performance. It is seen that the benefit from user CO operation decreases as the number of mobile users increases. Specifically, at k = 10, the cooperation exhibits a similar performance as the direct transmission. Figure 4: Average bit error rate performance in a K-user random cooperative network with equal transmission power and identical crosscorrelations
Coo peration pairs are picked up from the network inde- pendently on their locations. The set Sy contains all oddly indexed nodes and set Sp contains all evenly indexed nodes. U, coo perates with Uj;,+1 if k is aodd number. Fig.4 shows the average bit error rate versus the number of mobile users K, with identical crosscorrelation p = 1/31. In order to exploit the additional diversity gain from user cooperation, it is important to ensure a relative low average BER at re- lay nod es, such that they can reliably detect their sources and forward the information bits. On the contrary, if the inter-user channel quality is very poor, the benefit from co- operation is limited. For comparison, we present the per- formance with either a MMSE detector or a matched filter being used at relay nodes, and MMSE detector at the base station. We observe that the average BER is robust to the number of users if MMSE detection is adopted at each re- lay. However, in the case of matched filter, MAI caused by non-orthogonal spreading codes adversely affects the av- erage BER performance. It is seen that the benefit from user CO operation decreases as the number of mobile users increases. Specifically, at k = 10, the cooperation exhibits a similar performance as the direct transmission. Figure 4: Average bit error rate performance in a K-user random cooperative network with equal transmission power and identical crosscorrelations
Related topics:
Fading ChannelProbabilityWireless Communications and NetworkingBit Error RateCooperative TransmissionSpread Spectrum CommunicationSpatial DiversityCode Division Multiple AccessCooperative DiversityMinimum Mean Square Error
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