23-04-2011, 02:59 PM
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HISTORY OF MIMO TECHNOLOGY
In radio, multiple-input and multiple-output, or MIMO (commonly pronounced my-moh or me-moh), 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.
MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and page link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and page link reliability or diversity (reduced fading). Because of these properties, MIMO is a current theme of international wireless research.
The increasing demand for capacity in wireless systems has motivated considerable research aimed at achieving higher throughput on a given bandwidth. One important recent discovery shows that in a multipath environment, the use of space-time coding with multiple antennas on both ends of the page link can increase the capacity of the wireless channel.
Assessing the performance of these algorithms requires detailed understanding of multiple-input multiple-output (MIMO) channels as well as models that capture their complex spatial behavior. In this work, we discuss data from an experimental platform designed to measure the transfer matrix for indoor MIMO channels. The data is used to demonstrate the effect of polarization and array size on the achievable capacity for MIMO architectures. A propagation-based statistical model is shown to provide results that match closely with measured observations.
Background technologies
The earliest ideas in this field go back to work by A.R. Kaye and D.A. George (1970) and W. van Etten (1975, 1976). Jack Winters and Jack Salz at Bell Laboratories published several papers on beam forming related applications in 1984 and 1986.[1]
Principle
Arogyaswami Paulraj and Thomas Kailath proposed the concept of spatial multiplexing (SM) using MIMO in 1993. Their US Patent No. 5,345,599 on Spatial Multiplexing issued 1994[2] emphasized applications to wireless broadcast.
In 1996, Greg Raleigh and Gerard J. Foschini refined new approaches to MIMO technology, considering a configuration where multiple transmit antennas are co-located at one transmitter to improve the page link throughput effectively. Bell Labs was the first to demonstrate a laboratory prototype of spatial multiplexing in 1998, where spatial multiplexing is a principal technology to improve the performance of MIMO communication systems.
Wireless standards
See also: MIMO technology in WiMAX and MIMO technology in 3G mobile standards
In the commercial arena, Iospan Wireless Inc. developed the first commercial system in 2001 that used MIMO with Orthogonal frequency-division multiple access technology (MIMO-OFDMA). Iospan technology supported both diversity coding and spatial multiplexing. In 2005, Airgo Networks had developed an IEEE 802.11n precursor implementation based on their patents on MIMO. Following that in 2006, several companies (including at least Broadcom, Intel, and Marvell) have fielded a MIMO-OFDM solution based on a pre-standard for 802.11n WiFi standard. Also in 2006, several companies (Beceem Communications, Samsung, Runcom Technologies, etc.) have developed MIMO-OFDMA based solutions for IEEE 802.16e WiMAX broadband mobile standard. All upcoming 4G systems will also employ MIMO technology. Several research groups have demonstrated over 1 Gbit/s prototypes.
2. INTRODUCTION OF MIMO TECHNOLGY
In radio, multiple-input and multiple-output, or MIMO (commonly pronounced my-moh or me-moh), 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. Note that the terms input and output refer to the radio channel carrying the signal, not to the devices having antennas.
MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and page link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and page link reliability or diversity (reduced fading). Because of these properties, MIMO is an important part of modern wireless communication standards such as IEEE 802.11n (Wifi), 4G, 3GPP Long Term Evolution, WiMAX and HSPA+.
Fig. 1 Understanding of SISO, SIMO, MISO and MIMO (note that the terms input and output refer to the radio channel carrying the signal, not to the devices having antennas)
High data rate wireless communications, nearing 1-Gb/s transmission rates, is of interest in emerging wireless local area networks and home audio/visual networks. Designing very high speed wireless links that offer good quality-of-service and range capability in non-line-of-sight (NLOS) environments constitutes a significant research and engineering challenge. Ignoring fading in NLOS environments, we can, in principle, meet the 1-Gb/s data rate requirement.
With a single-transmit single-receive antenna wireless system if the product of bandwidth (measured in hertz) and spectral efficiency (measured in bits per second per hertz) is equal to 10 . As we shall outline in this paper, a variety of cost, technology and regulatory constraints make such a brute force solution unattractive if not impossible. The use of multiple antennas at transmitter and receiver, popularly known as multiple-input multiple-output (MIMO) wireless is an emerging cost-effective technology that offers substantial leverages in making 1-Gb/s wireless links a reality. This paper provides an overview of MIMO wireless technology covering
channel models, performance limits, coding, and transceiver design
Digital communication using MIMO (multiple-input multiple-output) or also called volume to volume wireless links is emerging as one of the most promising research areas in wireless communications. In wireless MIMO the transmitting end as well as the receiving end is equipped with multiple antenna elements, as such MIMO can be viewed as an extension of the very popular ‘smart antennas’. In MIMO though the transmit antennas and receive antennas are jointly combined in such a way that the quality (Bit Error Rate) or the rate (Bit/Sec) of the communication is improved. At the system level, careful design of MIMO signal processing and coding algorithms can help increase dramatically capacity and coverage and thus can improve the economics of network deployment for operators. Today, MIMO wireless is widely recognized as one of three or four key technologies in the forthcoming high-speed high-spectrum efficiency wireless networks (4G, and to some extent 3G). Applications also exist in fixed wireless.
Progress in MIMO research poses strong scientific challenges in the areas of modeling (of mobile space-time wireless channels), information theory (coding, channel capacity and other bounds on information transfer rates), signal processing (signaling and modulation design, receiver algorithms), and finally the design of the wireless fixed or mobile networks that will incorporate those MIMO links in order to maximize their gain. More specifically, joint design of sensible multiple access solutions (CDMA, OFDMA, TDMA and variants) as well as medium access (MAC) protocol for wireless MIMO is challenging.
3. Functions of MIMO
MIMO can be sub-divided into three main categories, preceding, spatial multiplexing or SM, and diversity coding.
Precoding is multi-stream beam forming, in the narrowest definition. In more general terms, it is considered to be all spatial processing that occurs at the transmitter. In (single-layer) beam forming, the same signal is emitted from each of the transmit antennas with appropriate phase (and sometimes gain) weighting such that the signal power is maximized at the receiver input. The benefits of beam forming are to increase the received signal gain, by making signals emitted from different antennas add up constructively, and to reduce the multipath fading effect. In the absence of scattering, beam forming results in a well defined directional pattern, but in typical cellular conventional beams are not a good analogy. When the receiver has multiple antennas, the transmit beam forming cannot simultaneously maximize the signal level at all of the receive antennas, and preceding with multiple streams is used. Note that preceding requires knowledge of channel state information (CSI) at the transmitter.
Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser in the number of antennas at the transmitter or receiver. Spatial multiplexing can be used with or without transmit channel knowledge. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access. By scheduling receivers with different spatial signatures, good separability can be assured.
Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beam forming or array gain from diversity coding.
Spatial multiplexing can also be combined with preceding when the channel is known at the transmitter or combined with diversity coding when decoding reliability is in trade-off.
HISTORY OF MIMO TECHNOLOGY
In radio, multiple-input and multiple-output, or MIMO (commonly pronounced my-moh or me-moh), 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.
MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and page link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and page link reliability or diversity (reduced fading). Because of these properties, MIMO is a current theme of international wireless research.
The increasing demand for capacity in wireless systems has motivated considerable research aimed at achieving higher throughput on a given bandwidth. One important recent discovery shows that in a multipath environment, the use of space-time coding with multiple antennas on both ends of the page link can increase the capacity of the wireless channel.
Assessing the performance of these algorithms requires detailed understanding of multiple-input multiple-output (MIMO) channels as well as models that capture their complex spatial behavior. In this work, we discuss data from an experimental platform designed to measure the transfer matrix for indoor MIMO channels. The data is used to demonstrate the effect of polarization and array size on the achievable capacity for MIMO architectures. A propagation-based statistical model is shown to provide results that match closely with measured observations.
Background technologies
The earliest ideas in this field go back to work by A.R. Kaye and D.A. George (1970) and W. van Etten (1975, 1976). Jack Winters and Jack Salz at Bell Laboratories published several papers on beam forming related applications in 1984 and 1986.[1]
Principle
Arogyaswami Paulraj and Thomas Kailath proposed the concept of spatial multiplexing (SM) using MIMO in 1993. Their US Patent No. 5,345,599 on Spatial Multiplexing issued 1994[2] emphasized applications to wireless broadcast.
In 1996, Greg Raleigh and Gerard J. Foschini refined new approaches to MIMO technology, considering a configuration where multiple transmit antennas are co-located at one transmitter to improve the page link throughput effectively. Bell Labs was the first to demonstrate a laboratory prototype of spatial multiplexing in 1998, where spatial multiplexing is a principal technology to improve the performance of MIMO communication systems.
Wireless standards
See also: MIMO technology in WiMAX and MIMO technology in 3G mobile standards
In the commercial arena, Iospan Wireless Inc. developed the first commercial system in 2001 that used MIMO with Orthogonal frequency-division multiple access technology (MIMO-OFDMA). Iospan technology supported both diversity coding and spatial multiplexing. In 2005, Airgo Networks had developed an IEEE 802.11n precursor implementation based on their patents on MIMO. Following that in 2006, several companies (including at least Broadcom, Intel, and Marvell) have fielded a MIMO-OFDM solution based on a pre-standard for 802.11n WiFi standard. Also in 2006, several companies (Beceem Communications, Samsung, Runcom Technologies, etc.) have developed MIMO-OFDMA based solutions for IEEE 802.16e WiMAX broadband mobile standard. All upcoming 4G systems will also employ MIMO technology. Several research groups have demonstrated over 1 Gbit/s prototypes.
2. INTRODUCTION OF MIMO TECHNOLGY
In radio, multiple-input and multiple-output, or MIMO (commonly pronounced my-moh or me-moh), 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. Note that the terms input and output refer to the radio channel carrying the signal, not to the devices having antennas.
MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and page link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and page link reliability or diversity (reduced fading). Because of these properties, MIMO is an important part of modern wireless communication standards such as IEEE 802.11n (Wifi), 4G, 3GPP Long Term Evolution, WiMAX and HSPA+.
Fig. 1 Understanding of SISO, SIMO, MISO and MIMO (note that the terms input and output refer to the radio channel carrying the signal, not to the devices having antennas)
High data rate wireless communications, nearing 1-Gb/s transmission rates, is of interest in emerging wireless local area networks and home audio/visual networks. Designing very high speed wireless links that offer good quality-of-service and range capability in non-line-of-sight (NLOS) environments constitutes a significant research and engineering challenge. Ignoring fading in NLOS environments, we can, in principle, meet the 1-Gb/s data rate requirement.
With a single-transmit single-receive antenna wireless system if the product of bandwidth (measured in hertz) and spectral efficiency (measured in bits per second per hertz) is equal to 10 . As we shall outline in this paper, a variety of cost, technology and regulatory constraints make such a brute force solution unattractive if not impossible. The use of multiple antennas at transmitter and receiver, popularly known as multiple-input multiple-output (MIMO) wireless is an emerging cost-effective technology that offers substantial leverages in making 1-Gb/s wireless links a reality. This paper provides an overview of MIMO wireless technology covering
channel models, performance limits, coding, and transceiver design
Digital communication using MIMO (multiple-input multiple-output) or also called volume to volume wireless links is emerging as one of the most promising research areas in wireless communications. In wireless MIMO the transmitting end as well as the receiving end is equipped with multiple antenna elements, as such MIMO can be viewed as an extension of the very popular ‘smart antennas’. In MIMO though the transmit antennas and receive antennas are jointly combined in such a way that the quality (Bit Error Rate) or the rate (Bit/Sec) of the communication is improved. At the system level, careful design of MIMO signal processing and coding algorithms can help increase dramatically capacity and coverage and thus can improve the economics of network deployment for operators. Today, MIMO wireless is widely recognized as one of three or four key technologies in the forthcoming high-speed high-spectrum efficiency wireless networks (4G, and to some extent 3G). Applications also exist in fixed wireless.
Progress in MIMO research poses strong scientific challenges in the areas of modeling (of mobile space-time wireless channels), information theory (coding, channel capacity and other bounds on information transfer rates), signal processing (signaling and modulation design, receiver algorithms), and finally the design of the wireless fixed or mobile networks that will incorporate those MIMO links in order to maximize their gain. More specifically, joint design of sensible multiple access solutions (CDMA, OFDMA, TDMA and variants) as well as medium access (MAC) protocol for wireless MIMO is challenging.
3. Functions of MIMO
MIMO can be sub-divided into three main categories, preceding, spatial multiplexing or SM, and diversity coding.
Precoding is multi-stream beam forming, in the narrowest definition. In more general terms, it is considered to be all spatial processing that occurs at the transmitter. In (single-layer) beam forming, the same signal is emitted from each of the transmit antennas with appropriate phase (and sometimes gain) weighting such that the signal power is maximized at the receiver input. The benefits of beam forming are to increase the received signal gain, by making signals emitted from different antennas add up constructively, and to reduce the multipath fading effect. In the absence of scattering, beam forming results in a well defined directional pattern, but in typical cellular conventional beams are not a good analogy. When the receiver has multiple antennas, the transmit beam forming cannot simultaneously maximize the signal level at all of the receive antennas, and preceding with multiple streams is used. Note that preceding requires knowledge of channel state information (CSI) at the transmitter.
Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser in the number of antennas at the transmitter or receiver. Spatial multiplexing can be used with or without transmit channel knowledge. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access. By scheduling receivers with different spatial signatures, good separability can be assured.
Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beam forming or array gain from diversity coding.
Spatial multiplexing can also be combined with preceding when the channel is known at the transmitter or combined with diversity coding when decoding reliability is in trade-off.
