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Cooperative Diversity
Cooperative diversity is a cooperative multiple antenna technique for improving or maximising total network channel capacities for any given set of bandwidths which exploits user diversity by decoding the combined signal of the relayed signal and the direct signal in wireless multihop networks. A conventional single hop system uses direct transmission where a receiver decodes the information only based on the direct signal while regarding the relayed signal as interference, whereas the cooperative diversity considers the other signal as contribution. That is, cooperative diversity decodes the information from the combination of two signals. Hence, it can be seen that cooperative diversity is an antenna diversity that uses distributed antennas belonging to each node in a wireless network. Note that user cooperation is another definition of cooperative diversity. ''User cooperation'' considers an additional fact that each user relays the other user's signal while cooperative diversit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesh Network
A mesh network is a local area network topology in which the infrastructure nodes (i.e. bridges, switches, and other infrastructure devices) connect directly, dynamically and non-hierarchically to as many other nodes as possible and cooperate with one another to efficiently route data to and from clients. This lack of dependency on one node allows for every node to participate in the relay of information. Mesh networks dynamically self-organize and self-configure, which can reduce installation overhead. The ability to self-configure enables dynamic distribution of workloads, particularly in the event a few nodes should fail. This in turn contributes to fault-tolerance and reduced maintenance costs. Mesh topology may be contrasted with conventional star/tree local network topologies in which the bridges/switches are directly linked to only a small subset of other bridges/switches, and the links between these infrastructure neighbours are hierarchical. While star-and-tree topologi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmit Diversity
Transmit diversity is radio communication using signals that originate from two or more independent sources that have been modulated with identical information-bearing signals and that may vary in their transmission characteristics at any given instant. It can help overcome the effects of fading, outages, and circuit failures. When using diversity transmission and reception, the amount of received signal improvement depends on the independence of the fading characteristics of the signal as well as circuit outages and failures. Considering antenna diversity, in many systems additional antennas may be expensive or impractical at the remote or even at the base station. In these cases, transmit diversity can be used to provide diversity benefit at a receiver with multiple transmit antennas only. With transmit diversity, multiple antennas transmit delayed versions of a signal, creating frequency-selective fading, which is equalized at the receiver to provide diversity gain. Sinc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity Combining
Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal. Various techniques Various diversity combining techniques can be distinguished: * Equal-gain combining: All the received signals are summed coherently. * Maximal-ratio combining is often used in large phased-array systems: The received signals are weighted with respect to their SNR and then summed. The resulting SNR yields \sum_^SNR_k where SNR_k is SNR of the received signal k. * Switched combining: The receiver switches to another signal when the currently selected signal drops below a predefined threshold. This is also often called "Scanning Combining". * Selection combining: Of the N received signals, the strongest signal is selected. When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be \sum_^\frac, expressed as a power ratio. Therefore, any additional gain diminishes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multi-user MIMO
Multi-user MIMO (MU-MIMO) is a set of multiple-input and multiple-output (MIMO) technologies for multipath wireless communication, in which multiple users or terminals, each radioing over one or more antennas, communicate with one another. In contrast, single-user MIMO (SU-MIMO) involves a single multi-antenna-equipped user or terminal communicating with precisely one other similarly equipped node. Analogous to how OFDMA adds multiple-access capability to OFDM in the cellular-communications realm, MU-MIMO adds multiple-user capability to MIMO in the wireless realm. SDMA,N. JindalMIMO Broadcast Channels with Finite Rate Feedback IEEE Transactions on Information Theory, vol. 52, no. 11, pp. 5045–5059, 2006.D. Gesbert, M. Kountouris, R.W. Heath Jr., C.-B. Chae, and T. SälzerShifting the MIMO Paradigm IEEE Signal Processing Magazine, vol. 24, no. 5, pp. 36-46, 2007.R. Tweg, R. Alpert, H. Leizerovich, A. Steiner, E. Levitan, E. Offir-Arad, A.B. Guy, B. Zickel, A. Aviram, A. Frieman, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiple-input Multiple-output Communications
In radio, multiple-input and multiple-output, or MIMO (), is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation. MIMO has become an essential element of wireless communication standards including IEEE 802.11n (Wi-Fi 4), IEEE 802.11ac (Wi-Fi 5), HSPA+ (3G), WiMAX, and Long Term Evolution (LTE). More recently, MIMO has been applied to power-line communication for three-wire installations as part of the ITU G.hn standard and of the HomePlug AV2 specification. At one time, in wireless the term "MIMO" referred to the use of multiple antennas at the transmitter and the receiver. In modern usage, "MIMO" specifically refers to a class of techniques for sending and receiving more than one data signal simultaneously over the same radio channel by exploiting multipath propagation. Additionally, modern MIMO usage often refers to multiple data signals sent to different receivers (with one or more rece ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space–time Code
A space–time code (STC) is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding. Space time codes may be split into two main types: *Space–time trellis code Space–time trellis codes (STTCs) are a type of space–time code used in multiple-antenna wireless communications. This scheme transmits multiple, redundant copies of a generalised TCM signal distributed over time and a number of antennas ('s ...s (STTCs) distribute a convolutional code, trellis code over multiple antennas and multiple time-slots and provide both coding gain and diversity reception, diversity gain. *Space–time block codes (STBCs) act on a block of data at once (similarly to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soft Handover
Soft handover or soft handoff refers to a feature used by the CDMA and W-CDMA standards, where a cell phone is simultaneously connected to two or more cells (or cell sectors) during a call. If the sectors are from the same physical cell site (a sectorised site), it is referred to as softer handoff. This technique is a form of mobile-assisted handover, for IS-95/CDMA2000 CDMA cell phones continuously make power measurements of a list of neighboring cell sites, and determine whether or not to request or end soft handover with the cell sectors on the list. Due to the properties of the CDMA signaling scheme, it is possible for a CDMA phone to simultaneously receive signals from two or more radio base stations that are transmitting the same bit stream (using different transmission codes) on the different physical channels in the same frequency bandwidth. If the signal power from two or more radio base stations is nearly the same, the phone receiver can combine the received signals in su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Single Frequency Networks
{{Unreferenced, date=January 2008 Dynamic Single Frequency Networks (DSFN) is a transmitter macrodiversity technique for OFDM based cellular networks. DSFN is based on the idea of single frequency networks (SFN), which is a group of radio transmitters that send the same signal simultaneously over the same frequency. The term originates from the broadcasting world, where a broadcast network is a group of transmitters that send the same TV or radio program. Digital wireless communication systems based on the OFDM modulation scheme are well-suited to SFN operation, since OFDM in combination with some forward error correction scheme can eliminate intersymbol interference and fading caused by multipath propagation without the use of complex equalization. The concept of DSFN implies the SFN grouping is changed dynamically over time, from timeslot to timeslot. The aim is to achieve efficient spectrum utilization for downlink unicast or multicast communication services in centrally contro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cooperative MIMO
In radio, cooperative multiple-input multiple-output (cooperative MIMO, CO-MIMO) is a technology that can effectively exploit the spatial domain of mobile fading channels to bring significant performance improvements to wireless communication systems. It is also called network MIMO, distributed MIMO, virtual MIMO, and virtual antenna arrays. Conventional MIMO systems, known as point-to-point MIMO or collocated MIMO, require both the transmitter and receiver of a communication link to be equipped with multiple antennas. While MIMO has become an essential element of wireless communication standards, including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi), HSPA+ (3G), WiMAX (4G), and Long-Term Evolution (4G), many wireless devices cannot support multiple antennas due to size, cost, and/or hardware limitations. More importantly, the separation between antennas on a mobile device and even on fixed radio platforms is often insufficient to allow meaningful performance gains. Furthermore, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cooperative Wireless Communications
In radio, cooperative multiple-input multiple-output (cooperative MIMO, CO-MIMO) is a technology that can effectively exploit the spatial domain of mobile fading channels to bring significant performance improvements to wireless communication systems. It is also called network MIMO, distributed MIMO, virtual MIMO, and virtual antenna arrays. Conventional MIMO systems, known as point-to-point MIMO or collocated MIMO, require both the transmitter and receiver of a communication link to be equipped with multiple antennas. While MIMO has become an essential element of wireless communication standards, including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi), HSPA+ (3G), WiMAX (4G), and Long-Term Evolution (4G), many wireless devices cannot support multiple antennas due to size, cost, and/or hardware limitations. More importantly, the separation between antennas on a mobile device and even on fixed radio platforms is often insufficient to allow meaningful performance gains. Furthermore, as t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wireless Ad Hoc Network
A wireless ad hoc network (WANET) or mobile ad hoc network (MANET) is a decentralized type of wireless network. The network is ad hoc because it does not rely on a pre-existing infrastructure, such as routers in wired networks or access points in wireless networks. Instead, each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity and the routing algorithm in use. In the Windows operating system, ad hoc is a communication mode (setting) that allows computers to directly communicate with each other without a router. Wireless mobile ad hoc networks are self-configuring, dynamic networks in which nodes are free to move. Such wireless networks lack the complexities of infrastructure setup and administration, enabling devices to create and join networks "on the fly". Each device in a MANET is free to move independently in any direction, and will therefore change it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
