As far as the development of wireless communications, the demand for wireless transmission of data rates and quality of services is even increasing. Therefore expanding the channel capacity and improving the communication quality of the new technology is an important topic of academic concern.
MULTIPLE-INPUT, MULTIPLE-OUTPUT (MIMO) TECHNOLOGY
Utilizing multiple-input, multiple-output (MIMO) technology can make full use of space resources without increasing the system bandwidth. Also the total transmit power of the antenna can be effective against the impact of wireless channel fading and greatly improve the communication system spectral efficiency and channel capacity. This is a new generation wireless mobile communication systems used in critical technologies. Foschini, Gans
And Telatar understand from the perspective of information theory to study the channel capacity of MIMO systems, and they indicated that: In certain conditions, the use of MIMO systems can greatly increase the channel capacity, and the channel capacity for growth and a smaller value is proportional to the number of transmitting and receiving antennas. Although the MIMO technology can provide space diversity gain, in certain applications, due to the terminal size, cost and hardware constraints, it is not suitable for users to use multiple antennas, which limits the mobile terminal to obtain space diversity gain capability.PRACTICAL IMPLIMENTATION-COOPERATIVE DIVERSITY
Multi-path fading is an important factor affecting the performance of mobile wireless communication. SENDONARIS proposed the concept of cooperative diversity . Cooperative Diversity is an effective mean to resistance multi-path fading. The basic idea of cooperative diversity is: Multiple users by sharing the network of antennas, forming a virtual antenna array, so as to achieve the signal transmission and reception space diversity. As the different positions of individual users in network, among them the formation of the communication channel independent of each other, the transmitter launch copies of multiple signals through the independent channel to reach the receiver so that generate diversity gain. As collaborative partners in Cooperative Diversity share their antennas, so as to constitute a virtual MMIO multi-antenna systems. In this sense, cooperative diversity provides a new alternative way to achieve the MIMO multiple antenna technology.
The idea of cooperative diversity is from relay channel. The difference between them is: in cooperative diversity network, each user must not only transmit their information, but also to help its partners relay transmit information. In other words, each user should not only act as a source of role, but also play a relay role. Three-terminal relay channel model is given by van der Meulen first. COVER and E1  investigated the discrete memoryless relay channels and Gaussian relay channel, and determined the capacity of degraded relay channel and they proposed three different random coding method. LANMAN and WORNELL[7,8] based on one random coding method, progressed Amplify-and-Forward(AF) and Decode-and-Forward(DF) schemes. HUNTER AND NOSRATINIA based on DF protocol, introduced channel coding, and designed Coded Cooperation (CC) protocol.Cooperative diversity protocol
Shown in Figure 2, in the DF protocol, relay users decode the signal transmitted by source users, and re-send the decoded information to the next relay user or the destination. Sendonaris analyzed the code division multiple access (CDMA) system, and achieved Code Division Multiple Access of DF relay . Sendonaris analyzed the situation of two users as a pair of cooperation partner, and pointed out that each duration is divided into three sub-periods, in the first and second sub-period, each user send their own signals, and then, each user detect other user's second bit. In the third sub-period, the two users send a linear combination of their own second bit and their partner second bit, and multiply their respective spreading code.SELECTION decode-and-forward (DF)
As far as we described above is fixed DF, now let me describe a more practical DF scheme, which is named selection decode-and-forward. The selection DF scheme was proposed by LANEMAN. He pointed out that only when the instantaneous signal to noise ratio (SNR) among users is relatively high, the users decode and forward data from partners, while when the instantaneous signal to noise ratio (SNR) among users is relatively low, users are non-cooperative. Selection DF scheme can be seen as an extension of fixed DF scheme. Selection DF scheme is based on the state of the channel between users to decide whether to cooperate, and this technology can be also used in the AF scheme.
HUNTER combined the channel coding with cooperative communication, and proposed the coded cooperation (CC) protocol . In CC protocol, Source data is divided into several blocks, and each block of data attached to a cyclic redundancy check (CRC) code.Outage probability analysis
David Tse firstly defined the outage probability . According to the joint source-channel coding theorem, the error-free decoding required transmission rate R is less than real-time channel capacity, C. As a result, when the transmission rate R is greater than the channel capacity, C, no matter what encoding, it is impossible to achieve error-free transmission, which is called outage event. Outage probability is defined as the probability of outage event. Outage probability does not consider the specific encoding method, and it shows the probability of channel fading rate is lower than a threshold.
Outage probability plays a very important role in cooperative communication networks.DIVERSITY TECHNOLOGY
In the Raleigh fading channel, when the content of channel fading is below a certain threshold, the receiving node cannot be properly recovered original message. Therefore the system cannot communicate properly. In order to maintain reliable communication, reduce the outage probability of communication system, diversity techniques have emerged. Diversity is the use of different channels to receive a copy of the same signal. Ideally, these different channels independently of each other, so that the same signal can experience different fading. Without using diversity technology, the channel fading rate is below a certain threshold the probability of relatively large. By contrast, using diversity technology, the sum of the probability of each received signal power below a certain threshold would get smaller, which means that the system has a good performance of fading resistance. Diversity is divided into many forms, in this paper we apply the spatial diversity
- Foschini G J,Gans M J.On limits of wireless communication in a fading environment when using multiple antennas.Wireless Personal Communication,1998, 6(3):311~335
- Telatar L E.Capacity of multi-antenna Gaussian channels. European Trans. Telecomm,1999,10(6):585~595
- A. Sendonaris, E. Erkip, and B. Aazhang, "Increasing uplink capacityvia user cooperation diversity," in Proc. IEEE Int. Symp. InformationTheory (ISIT), Cambridge, MA, Aug. 1998, p. 156.
- E.C.vnaderMeulen,"Three?etmrinaleommunieationchannels, vol.3, PP.120-154,1971.
- TM.Cover and A.A.EIGmaal,"Cpaaeiyttheoermsofrtheerl?ehnnael, IEEETrnas. vol.25,PP·572-584,SeP1979.
- A. Nosratinia, T. Hunter, and A. Hedayat, "Cooperative communication in wireless networks," IEEE Commun. Mag, vol. 42, pp. 74-80, 2004.
- DvaidTse,PmarodViswnaath,"FundmaentalsofWierlessCommunieation," Cmabridge UnivesriytPress,2004
- Sendonaris A,Erkip E,and Aazhang B.User cooperation diversity_Part I:System description.IEEE Transaction on Communications,2003,51(11):1927~1938
- Sendonaris A,Erkip E,and Aazhang B.User cooperation diversity_Part II:Implementation aspects and performance analysis.IEEE Transaction onCommunications,2003,51(11):1939~1948
- Hunter T E,Nosratinia A.Cooperative diversity through coding.In:Proc.IEEE International Symposium on Information Theory(ISIT).Laussane,Switzerland: 2002.220
Article name: Wireless transmission essay, research paper, dissertation