Multi-user MIMO
Encyclopedia
In radio
, multi-user MIMO (MU-MIMO) is a set of advanced MIMO
, multiple-input and multiple-output , technologies that exploit the availability of multiple independent radio terminals in order to enhance the communication capabilities of each individual terminal. To contrast, single-user MIMO only considers access to the multiple antennas that are physically connected to each individual terminal. MU-MIMO can be seen as the extended concept of space-division multiple access (SDMA) which allows a terminal to transmit (or receive) signal to (or from) multiple users in the same band simultaneously. PU2RC
is a fundamental and practical MU-MIMO technology for broadcast and multiple access wireless communications.
Like the relationship between OFDM and OFDMA
, MU-MIMO (and, similarly, SDMA) can be thought of as an extension of MIMO applied in various ways as a multiple access strategy. A significant difference is that the performance of MU-MIMO relies on precoding
capability than OFDMA so that if the transmitter does not use precoding, the performance advantage of MU-MIMO is not achievable.
Multiple access MIMO, MIMO-SDMA, many transmit antenna MIMO-SDMA, Cooperative MIMO, Network MIMO and Ad-hoc MIMO are all family terminologies within MU-MIMO, as each of those technologies leverages multiple users as a degree of freedom in achieving successful radio transmission.
Here, based on the literature, we summarize a number of advanced MIMO techniques that leverage multiple users:
To remove ambiguity of the words receiver and transmitter, we can adopt the terms access point (AP; or, base station), and user. An AP is the transmitter and a user is the receiver for downlink environments, whereas an AP is the receiver and a user is the transmitter for uplink environments. Homogeneous networks are somewhat freed from this distinction.
systems, the base station
has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. This results in wasting power on transmissions when there are no mobile units to reach, in addition to causing interference
for adjacent cells using the same frequency, so called co-channel cells. Likewise, in reception, the antenna
receives signals coming from all directions including noise and interference signals. By using smart antenna
technology and by leveraging the spatial location of mobile units within the cell, space-division multiple access techniques offer attractive performance enhancements. The radiation pattern
of the base station, both in transmission and reception, is adapted to each user to obtain highest gain in the direction of that user. This is often done using phased array
techniques.
In GSM cellular networks, the base station is aware of the mobile phone's position by use of a technique called Timing Advance (TA). The Base Transceiver Station (BTS) can determine how distant the Mobile Station (MS) is by interpreting the reported TA. This information, along with other parameters, can then be used to power down the BTS or MS, if a power control feature is implemented in the network. The power control in either BTS or MS is implemented in most modern networks, especially on the MS, as this ensures a better battery life for the MS and thus a better user experience (in that the need to charge the battery becomes less frequent). This is why it may actually be safer to have a BTS close to you as your MS will be powered down as much as possible. For example, there is more power being transmitted from the MS than what you would receive from the BTS even if you are 6 m away from a mast. However, this estimation might not consider all the MS's that a particular BTS is supporting with EM radiation at any given time.
New SDMA: MU-MIMO, Network MIMO (COMP), Remote radio equipments
New beamforming: linear beamforming such as MF, ZF and MMSE and nonlinear beamforming such as THP, VP, and DPC
New antenna array: direct, remote and wireless antenna array
Direct antenna array: linear and 3d phased array, new structure array, and dynamic antenna array
Remote and wireless antenna array: distributed antenna array and cooperative beamforming
MIMO broadcast represents a MIMO downlink case in a single sender to multiple receiver wireless network. Examples of advanced transmit processing for MIMO BC are interference aware precoding
and SDMA-based downlink user scheduling. For advanced transmit processing, the transmitter has to know the channel state information
at the transmitter (CSIT). That is, knowledge of CSIT allows throughput improvement, and methods to obtain CSIT become of significant importance. MIMO BC systems have an outstanding advantage over point-to-point MIMO systems, especially when the number of transmit antennas at the transmitter, or AP, is larger than the number of receiver antennas at each receiver (user).
at the receiver (CSIR). Knowing CSIR is generally easier than knowing CSIT. However, to know CSIT costs a lot of uplink resources to transmit dedicated pilots from each user to the AP. MIMO MAC systems outperforms point-to-point MIMO systems especially when the number of receiver antennas at an AP is larger than the number of transmit antennas at each user.
. It can be described as a form of macro-diversity, used for example in soft handover
. Cooperative MISO corresponds to transmitter macro-diversity or simulcasting. A simple form that does not require any advanced signal processing is single frequency networks (SFN), used especially in wireless broadcasing. SFNs combined with channel adaptive or traffic adaptive scheduling is called dynamic single frequency networks (DSFN).
CO-MIMO is a technique useful for future cellular networks which consider wireless mesh networking or wireless ad-hoc networking. In wireless ad-hoc network
s, multiple transmit nodes communicate with multiple receive nodes. To optimize the capacity of Ad-hoc channels, MIMO concepts and techniques can be applied to multiple links between the transmit and receive node clusters. Contrasted to multiple antennas in a single-user MIMO transceiver, participating nodes and their antennas are located in a distributed manner. So, to achieve the capacity of this network, techniques to manage distributed radio resources are essential. Strategies such as autonomous interference cognition
, node cooperation, and network coding with dirty paper coding (DPC) have been suggested as solutions to optimize wireless network capacity.
Of analogical interest here may be the comparison between the evolution of computing cores and mobile antennas. To wit, a single high performance core is the first generation of CPU core evolution, progressing to a few cores, and then to many cores in a centralized fashion as the second step—the recent environment. It is anticipated that it will be common for cooperative work to proceed from multiple cores owned by different users, made available to the individual user in return for help with others' information processing. Such catchphrases include ambient intelligence
, wireless ubiquitous computing
, and the semantic web
.
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
, multi-user MIMO (MU-MIMO) is a set of advanced MIMO
MIMO
In radio, multiple-input and multiple-output, or MIMO , is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology...
, multiple-input and multiple-output , technologies that exploit the availability of multiple independent radio terminals in order to enhance the communication capabilities of each individual terminal. To contrast, single-user MIMO only considers access to the multiple antennas that are physically connected to each individual terminal. MU-MIMO can be seen as the extended concept of space-division multiple access (SDMA) which allows a terminal to transmit (or receive) signal to (or from) multiple users in the same band simultaneously. PU2RC
PU2RC
Per-User Unitary Rate Control is the advanced multi-user MIMO technique which utilizes the concept of both pre-coding matrices and scheduling to enhance the system performance of multiple antenna wireless networks....
is a fundamental and practical MU-MIMO technology for broadcast and multiple access wireless communications.
Like the relationship between OFDM and OFDMA
OFDMA
Orthogonal Frequency-Division Multiple Access is a multi-user version of the popular Orthogonal frequency-division multiplexing digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users as shown in the illustration below...
, MU-MIMO (and, similarly, SDMA) can be thought of as an extension of MIMO applied in various ways as a multiple access strategy. A significant difference is that the performance of MU-MIMO relies on precoding
Precoding
Precoding is a generalization of beamforming to support multi-layer transmission in multi-antenna wireless communications. In conventional single-layer beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting such that the signal power is maximized at...
capability than OFDMA so that if the transmitter does not use precoding, the performance advantage of MU-MIMO is not achievable.
Multiple access MIMO, MIMO-SDMA, many transmit antenna MIMO-SDMA, Cooperative MIMO, Network MIMO and Ad-hoc MIMO are all family terminologies within MU-MIMO, as each of those technologies leverages multiple users as a degree of freedom in achieving successful radio transmission.
MIMO
To achieve MIMO from a conventional SISO system, several technologies have been proposed.- BeamformingBeamformingBeamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
is known as antenna array signal processing, where every antenna element is separated from its nearest element by half of the transmit signal wavelength. - Space-time coding/processingSpace–time codeA space–time code is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas...
performs antenna diversity with multiple antennas at either transmitter or receiver side or both sides, where every antenna element is separated from its nearest element by around 4 to 10 times the wavelength to keep the signal through each multi-path independent. The distance between two adjacent antenna elements is relying on the angular spread of the beam signal. - SDMA is a common and typical multiple input multiple output scheme in cellular wireless systems. SDMA is often referred to as simply a MIMO system since the half port of a SDMA system also consists of multiple users. Although SDMA is indeed a MIMO technique, MIMO is not necessarily SDMA.
- Spatial multiplexingSpatial multiplexingSpatial multiplexing is a transmission technique in MIMO wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas...
is performed by multiple antennas equipped at both a transmitter and a receiver front end. - Cooperation are known as network MIMO systems, distributed MIMO systems or virtual antenna array systems. Mobile devices use the partnered mobile devices' antennas, antenna arrays, or antenna elements as virtual antennas.
- Combinations of above techniques, etc.
MIMO enhancement
Enhancement techniques can be categorized into evolutionary and revolutionary approaches:- Evolutionary approaches:
- Use an existing technique with enhanced PHY capabilities, perhaps a 16×16 array configuration, or
- Use new MIMO algorithms such as precoding or multi-user scheduling at the transmitter.
- Revolutionary approaches: developing fundamentally new MIMO concepts. Examples of revolution approaches are cooperative and virtual antenna MIMO and intelligent spatial processing such as RADARRadarRadar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
beamformingBeamformingBeamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
.
Here, based on the literature, we summarize a number of advanced MIMO techniques that leverage multiple users:
- Cross-layer MIMO: Scheduling, etc.
- Advanced decoding MIMO: Multi-user detection such as MLD.
- BeamformingBeamformingBeamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
and SDMASpace-division multiple accessSpace-Division Multiple Access is a channel access method based on creating parallel spatial pipes next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems...
: widely known multi-user MIMO scheme. - Infrared/Non-infrared network optimization.
- Network MIMO (Net-MIMO).
- Cognitive MIMO based on intelligent techniques.
- Cooperative/competitive MIMO.
- CooperationCooperationCooperation or co-operation is the process of working or acting together. In its simplest form it involves things working in harmony, side by side, while in its more complicated forms, it can involve something as complex as the inner workings of a human being or even the social patterns of a...
: DPCDirty paper codingIn telecommunications, dirty paper coding is a technique for efficient transmission of digital data through a channel subjected to some interference known to the transmitter...
, Wyner-Ziv, etc. - Competitive: Game theoryGame theoryGame theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
, autonomous packets, implicit MAC fairness, etc.
MU-MIMO
Multi-user MIMO can leverage multiple users as spatially distributed transmission resources, at the cost of somewhat more expensive signal processing. In comparison, conventional, or single-user MIMO considers only local device multiple antenna dimensions. Multi-user MIMO algorithms are developed to enhance MIMO systems when the number of users, or connections, numbers greater than one (admittedly, a useful concept). Multi-user MIMO can be generalized into two categories: MIMO broadcast channels (MIMO BC) and MIMO multiple access channels (MIMO MAC) for downlink and uplink situations, respectively. Single-user MIMO can be represented as point-to-point, pairwise MIMO.To remove ambiguity of the words receiver and transmitter, we can adopt the terms access point (AP; or, base station), and user. An AP is the transmitter and a user is the receiver for downlink environments, whereas an AP is the receiver and a user is the transmitter for uplink environments. Homogeneous networks are somewhat freed from this distinction.
Space-division multiple access
Space-Division Multiple Access (SDMA) enables creating parallel spatial pipes next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems. In traditional mobile cellular networkCellular network
A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...
systems, the base station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...
has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. This results in wasting power on transmissions when there are no mobile units to reach, in addition to causing interference
Co-channel interference
Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; four examples are listed here....
for adjacent cells using the same frequency, so called co-channel cells. Likewise, in reception, the antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
receives signals coming from all directions including noise and interference signals. By using smart antenna
Smart antenna
Smart antennas are antenna arrays with smart signal processing algorithms used to identify spatial signal signature such as the direction of arrival of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target...
technology and by leveraging the spatial location of mobile units within the cell, space-division multiple access techniques offer attractive performance enhancements. The radiation pattern
Radiation pattern
In the field of antenna design the term radiation pattern most commonly refers to the directional dependence of the strength of the radio waves from the antenna or other source ....
of the base station, both in transmission and reception, is adapted to each user to obtain highest gain in the direction of that user. This is often done using phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
techniques.
In GSM cellular networks, the base station is aware of the mobile phone's position by use of a technique called Timing Advance (TA). The Base Transceiver Station (BTS) can determine how distant the Mobile Station (MS) is by interpreting the reported TA. This information, along with other parameters, can then be used to power down the BTS or MS, if a power control feature is implemented in the network. The power control in either BTS or MS is implemented in most modern networks, especially on the MS, as this ensures a better battery life for the MS and thus a better user experience (in that the need to charge the battery becomes less frequent). This is why it may actually be safer to have a BTS close to you as your MS will be powered down as much as possible. For example, there is more power being transmitted from the MS than what you would receive from the BTS even if you are 6 m away from a mast. However, this estimation might not consider all the MS's that a particular BTS is supporting with EM radiation at any given time.
Many antennas
Many Antennas is a smart antenna technique, which overcomes the performance limitation of single user MIMO techniques. In cellular communications, the number of the maximum considered antennas for downlink is 2 and 4 to support LTE and IMT-A requirements, respectively. Since the available spectrum band will probably be limited while the requirement of data rate will continuously increase in beyond IMT-A to support the mobile multimedia services, it is highly probable that the number of transmit antennas at the base station must be increased up to 8 ~ 64 or more. The installation of many antennas at single base stations can have many challenges so it requires to develop several high technologies: new SDMA, new beamforming algorithm and new antenna array.New SDMA: MU-MIMO, Network MIMO (COMP), Remote radio equipments
New beamforming: linear beamforming such as MF, ZF and MMSE and nonlinear beamforming such as THP, VP, and DPC
New antenna array: direct, remote and wireless antenna array
Direct antenna array: linear and 3d phased array, new structure array, and dynamic antenna array
Remote and wireless antenna array: distributed antenna array and cooperative beamforming
MIMO broadcast (MIMO BC)
Precoding
Precoding is a generalization of beamforming to support multi-layer transmission in multi-antenna wireless communications. In conventional single-layer beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting such that the signal power is maximized at...
and SDMA-based downlink user scheduling. For advanced transmit processing, the transmitter has to know the channel state information
Channel state information
In wireless communications, channel state information refers to known channel properties of a communication link. This information describes how a signal propagates from the transmitter to the receiver and represents the combined effect of, for example, scattering, fading, and power decay with...
at the transmitter (CSIT). That is, knowledge of CSIT allows throughput improvement, and methods to obtain CSIT become of significant importance. MIMO BC systems have an outstanding advantage over point-to-point MIMO systems, especially when the number of transmit antennas at the transmitter, or AP, is larger than the number of receiver antennas at each receiver (user).
- Capacity approaching schemes: DPC precoding
- Near capacity: zero-forcing beamforming
MIMO MAC
Conversely, MIMO MAC represents a MIMO uplink case in the multiple sender to single receiver wireless network. Examples of advanced receive processing for MIMO MAC are joint interference cancellation and SDMA-based uplink user scheduling. For advanced receive processing, the receiver has to know the channel state informationChannel state information
In wireless communications, channel state information refers to known channel properties of a communication link. This information describes how a signal propagates from the transmitter to the receiver and represents the combined effect of, for example, scattering, fading, and power decay with...
at the receiver (CSIR). Knowing CSIR is generally easier than knowing CSIT. However, to know CSIT costs a lot of uplink resources to transmit dedicated pilots from each user to the AP. MIMO MAC systems outperforms point-to-point MIMO systems especially when the number of receiver antennas at an AP is larger than the number of transmit antennas at each user.
Cross-layer MIMO
Cross-layer MIMO enhances the performance of MIMO links by solving certain cross-layer problems that may occur when MIMO configurations are employed in a system. Cross-layer techniques can be used to enhance the performance of SISO links as well. Examples of cross-layer techniques are Joint Source-Channel Coding, Adaptive Modulation and Coding (AMC, or "Link Adaptation"), Hybrid ARQ (HARQ), and user scheduling.Multi-user to multi-user
The highly interconnected wireless ad-hoc network increases the flexibility of wireless networking at the cost of increased multi-user interference. To improve the interference immunity, PHY/MAC-layer protocols have evolved from competition based to cooperative based transmission and reception. Cooperative wireless communications can actually exploit interference, which includes self-interference and other user interference. In cooperative wireless communications, each node might use self-interference and other user interference to improve the performance of data encoding and decoding, whereas conventional nodes are generally directed to avoid the interference. For example, once strong interference is decodable, a node decodes and cancels the strong interference before decoding the self-signal. The mitigation of low Carrier over Interference (CoI) ratios can be implemented across PHY/MAC/Application network layers in cooperative systems.- Cooperative multiple antenna research — Apply multiple antenna technologies in situations with antennas distributed among neighboring wireless terminals.
- Cooperative diversityCooperative diversityCooperative 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...
— Achieve antenna diversityAntenna diversityAntenna diversity, also known as space diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight between transmitter and...
gain by the cooperation of distributed antennas belonging to each independent node. - Cooperative MIMO — Achieve MIMO advantages, including the spatial multiplexing gain, using the transmit or receiver cooperation of distributed antennas belonging to many different nodes.
- Cooperative diversity
- Cooperative relay — Apply cooperative concepts onto relay techniques, which is similar to cooperative diversity in terms of cooperative signalling. However, the main criterion of cooperative relay is to improve the tradeoff region between delay and performance, while that of cooperative diversity and MIMO is to improve the link and system performance at the expense of minimal cooperation loss.
- Relaying techniques for cooperation
- Store-and-forward (S&F), Amplify-and-forward (A&F), Decode-and-forward (D&F), Coded cooperation, Spatial coded cooperation, Compress-and-forward (C&F),Non-orthogonal methods
Cooperative MIMO (CO-MIMO)
CO-MIMO, also known as Network MIMO (Net-MIMO), or Ad-hoc MIMO, utilizes distributed antennas which belong to other users, while conventional MIMO, i.e., single-user MIMO, only employs antennas belonging to the local terminal. CO-MIMO improves the performance of a wireless network by introducing multiple antenna advantages, such as diversity, multiplexing and beamforming. If the main interest hinges on the diversity gain, it is known as cooperative diversityCooperative 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...
. It can be described as a form of macro-diversity, used for example in soft handover
Soft handover
Soft handover or soft handoff refers to a feature used by the CDMA and WCDMA standards, where a cell phone is simultaneously connected to two or more cells during a call. If the sectors are from the same physical cell site , it is referred to as softer handoff...
. Cooperative MISO corresponds to transmitter macro-diversity or simulcasting. A simple form that does not require any advanced signal processing is single frequency networks (SFN), used especially in wireless broadcasing. SFNs combined with channel adaptive or traffic adaptive scheduling is called dynamic single frequency networks (DSFN).
CO-MIMO is a technique useful for future cellular networks which consider wireless mesh networking or wireless ad-hoc networking. In wireless ad-hoc network
Wireless ad-hoc network
A wireless ad-hoc network is a decentralized type of wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks...
s, multiple transmit nodes communicate with multiple receive nodes. To optimize the capacity of Ad-hoc channels, MIMO concepts and techniques can be applied to multiple links between the transmit and receive node clusters. Contrasted to multiple antennas in a single-user MIMO transceiver, participating nodes and their antennas are located in a distributed manner. So, to achieve the capacity of this network, techniques to manage distributed radio resources are essential. Strategies such as autonomous interference cognition
Cognitive radio
A cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...
, node cooperation, and network coding with dirty paper coding (DPC) have been suggested as solutions to optimize wireless network capacity.
Of analogical interest here may be the comparison between the evolution of computing cores and mobile antennas. To wit, a single high performance core is the first generation of CPU core evolution, progressing to a few cores, and then to many cores in a centralized fashion as the second step—the recent environment. It is anticipated that it will be common for cooperative work to proceed from multiple cores owned by different users, made available to the individual user in return for help with others' information processing. Such catchphrases include ambient intelligence
Ambient intelligence
In computing, ambient intelligence refers to electronic environments that are sensitive and responsive to the presence of people. Ambient intelligence is a vision on the future of consumer electronics, telecommunications and computing that was originally developed in the late 1990s for the time...
, wireless ubiquitous computing
Ubiquitous computing
Ubiquitous computing is a post-desktop model of human-computer interaction in which information processing has been thoroughly integrated into everyday objects and activities. In the course of ordinary activities, someone "using" ubiquitous computing engages many computational devices and systems...
, and the semantic web
Semantic Web
The Semantic Web is a collaborative movement led by the World Wide Web Consortium that promotes common formats for data on the World Wide Web. By encouraging the inclusion of semantic content in web pages, the Semantic Web aims at converting the current web of unstructured documents into a "web of...
.
Related technologies
- Multiple-input multiple-output communications
- PrecodingPrecodingPrecoding is a generalization of beamforming to support multi-layer transmission in multi-antenna wireless communications. In conventional single-layer beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting such that the signal power is maximized at...
- Spatial multiplexingSpatial multiplexingSpatial multiplexing is a transmission technique in MIMO wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas...
- PU2RCPU2RCPer-User Unitary Rate Control is the advanced multi-user MIMO technique which utilizes the concept of both pre-coding matrices and scheduling to enhance the system performance of multiple antenna wireless networks....
- Mobile ad-hoc network
- Mesh network
- Wireless ad-hoc networkWireless ad-hoc networkA wireless ad-hoc network is a decentralized type of wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks...
- Distributed Antenna SystemDistributed Antenna SystemA Distributed Antenna System, or DAS, is a network of spatially separated antenna nodes connected to a common source via a transport medium that provides wireless service within a geographic area or structure...
- RADARRadarRadar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
Wireless standards
External links
- D. Gesbert, M. Kountouris, R. W. Heath, Jr., C.-B. Chae, and T. Salzer, Shifting the MIMO Paradigm: From Single User to Multiuser Communications, IEEE Signal Processing Magazine, vol. 24, no. 5, pp. 36–46, Oct., 2007.
- N. Jindal, MIMO Broadcast Channels with Finite Rate Feedback, IEEE Trans. Information Theory, Vol. 52, No. 11, pp. 5045–5059, Nov. 2006.
- C. B. Chae, D. Mazzarese, N. Jindal, and R. W. Heath, Jr., Coordinated Beamforming with Limited Feedback in the MIMO Broadcast Channel, IEEE Jour. on Selected Topics in Comm., 2008.
- P. Herhold, E. Zimmermann and G. Fettweis, On the Performance of Cooperative Amplify-and-Forward Relay Networks., 5th International ITG Conference on Source and Channel Coding (SCC), Erlangen, Germany, January 2004
- E. Zimmermann, P. Herhold and G. Fettweis, On the Performance of Cooperative Relaying Protocols in Wireless Networks., (Preprint version of the Journal article) European Transactions on Telecommunications (ETT), Volume 16, Issue 1 (January–February 2005), pages 17–35.
- S. Shattil, Cooperative Beamforming in Wireless Networks, U.S. Patent Appl. 11/187107, filed July 22, 2005.
- MIMO/SDMA and Beyond
- Game Theory Research Group
- Using Game Theory to Analyze Wireless Ad Hoc networks