• Transmit Diversity Vs Spatial Multiplexing
• Transmit Diversity And Receive Diversity
• Transmit Diversity Vs Spatial Multiplexing

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.Wikipedia

Transmit diversity can reduce the required E b /N 0 (or required transmit power per channel) and thus enhance the system capacity. Transmit diversity can be implemented in the following ways:. Multi-carrier transmit diversity. Antenna diversity can be implemented in a multicarrier forward link with no impact on the subscriber terminal, where. This paper presents a simple two-branch transmit diversity scheme. Using two transmit antennas and one receive antenna the scheme provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit antenna, and two receive antennas. It is also shown that the scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order.

• Phase modulation

  Modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave.Wikipedia

• Modulation

  Process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. Audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.Wikipedia

• Single-sideband modulation

  Type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently.Wikipedia

• Radio

  Technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz).Wikipedia

• Multipath propagation

  Propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings.Wikipedia

• Analog transmission

  Transmission method of conveying information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that information. Analog source signal, using an analog modulation method such as frequency modulation or amplitude modulation (AM), or no modulation at all.Wikipedia

• Diversity scheme

  In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts.Wikipedia

• Wireless telegraphy

  Transmission of telegraph signals by radio waves. Also used for other experimental technologies for transmitting telegraph signals without wires, such as electromagnetic induction, and ground conduction telegraph systems.Wikipedia

• Detector (radio)

  Device or circuit that extracts information from a modulated radio frequency current or voltage. The term dates from the first three decades of radio (1888-1918).Wikipedia

• Link budget

  Accounting of all of the power gains and losses that a communication signal experiences in a telecommunication system; from a transmitter, through a communication medium such as radio waves, cable, waveguide, or optical fiber, to the receiver. Equation giving the received power from the transmitter power, after the attenuation of the transmitted signal due to propagation, as well as the antenna gains and feedline and other losses, and amplification of the signal in the receiver or any repeaters it passes through.Wikipedia

• Radio scanner

  Radio receiver that can automatically tune, or scan, two or more discrete frequencies, stopping when it finds a signal on one of them and then continuing to scan other frequencies when the initial transmission ceases. Primarily intended for monitoring VHF and UHF landmobile radio systems, as opposed to, for instance, a receiver used to monitor international shortwave transmissions.Wikipedia

• Video modulation

  Strategy of transmitting video signal in the field of radio modulation and television technology. This strategy enables the video signal to be transmitted more efficiently through long distances.Wikipedia

• Radio transmitter design

  Electronic device which, when connected to an antenna, produces an electromagnetic signal such as in radio and television broadcasting, two way communications or radar. Heating devices, such as a microwave oven, although of similar design, are not usually called transmitters, in that they use the electromagnetic energy locally rather than transmitting it to another location.Wikipedia

• Rayleigh fading

  Statistical model for the effect of a propagation environment on a radio signal, such as that used by wireless devices. Rayleigh fading models assume that the magnitude of a signal that has passed through such a transmission medium (also called a communication channel) will vary randomly, or fade, according to a Rayleigh distribution — the radial component of the sum of two uncorrelated Gaussian random variables.Wikipedia

• Ring modulation

  Signal processing function, an implementation of frequency mixing, performed by creating multiple frequencies from those of the two signals, where one is typically a sine wave or another simple waveform and the other is the signal to be modulated. Electronic device for ring modulation.Wikipedia

• Radio receiver design

  Antenna in order to produce usable information such as audio. The complexity of a modern receiver and the possible range of circuitry and methods employed are more generally covered in electronics and communications engineering.Wikipedia

• Link adaptation

  Term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link (e.g. the pathloss, the interference due to signals coming from other transmitters, the sensitivity of the receiver, the available transmitter power margin, etc.). For example, WiMAX uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission.Wikipedia

• Radio resource management

  System level management of co-channel interference, radio resources, and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless local area networks, wireless sensor systems, and radio broadcasting networks. To utilize the limited radio-frequency spectrum resources and radio network infrastructure as efficiently as possible.Wikipedia

• Amplitude modulation

  Modulation technique used in electronic communication, most commonly for transmitting messages with a radio carrier wave. Varied in proportion to that of the message signal, such as an audio signal.Wikipedia

• Frequency modulation

  Encoding of information in a carrier wave by varying the instantaneous frequency of the wave. Used in telecommunications, radio broadcasting, signal processing, and computing.Wikipedia

• Spread spectrum

  Deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise, and jamming, to prevent detection, to limit power flux density (e.g., in satellite down links), and to enable multiple-access communications.Wikipedia

• Carrier-to-noise ratio

  Signal-to-noise ratio of a modulated signal. Used to distinguish the CNR of the radio frequency passband signal from the SNR of an analog base band message signal after demodulation, for example an audio frequency analog message signal.Wikipedia

• Cooperative diversity

  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.Wikipedia

• Shortwave radio

  Radio transmission using shortwave radio frequencies. No official definition of the band, but the range always includes all of the high frequency band , which extends from 3–30 MHz (100 to 10 metres); above the medium frequency band (MF), to the bottom of the VHF band.Wikipedia

• Through-the-earth mine communications

  Type of radio signalling used in mines and caves that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals. Restricted to line of sight to these antenna and repeaters systems.Wikipedia

• Time diversity

  Used in digital communication systems to combat that the transmissions channel may suffer from error bursts due to time-varying channel conditions. The error bursts may be caused by fading in combination with a moving receiver, transmitter or obstacle, or by intermittent electromagnetic interference, for example from crosstalk in a cable, or co-channel interference from radio transmitters.Wikipedia

• Intermodulation

  Amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency components will form additional components at frequencies that are not just at harmonic frequencies (integer multiples) of either, like harmonic distortion, but also at the sum and difference frequencies of the original frequencies and at sums and differences of multiples of those frequencies.Wikipedia

• Capture effect

  Phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency or channel will be demodulated. Defined as the complete suppression of the weaker signal at the receiver's limiter where the weaker signal is not amplified, but attenuated.Wikipedia

• Hierarchical modulation

  One of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before transmission. Particularly used to mitigate the cliff effect in digital television broadcast, particularly mobile TV, by providing a fallback signal in case of weak signals, allowing graceful degradation instead of complete signal loss.Wikipedia

• Listening station

  Facility used for military reconnaissance, especially telecommunications reconnaissance (also known as signals intelligence SIGINT) by 'intercepting' radio transmitter communications. Acoustic speech conversation, radio eavesdropping stations are used to eavesdrop on the information transmitted wirelessly using radio technology.Wikipedia

Sentences forTransmit diversity

• The 802.16 specification supports the Multiple-input and single-output (MISO) technique of Transmit Diversity, which is commonly referred to Space Time Code (STC).WiMAX MIMO-Wikipedia
• See also Modulation, Pulse compression, Spread spectrum, Transmit diversity, Ambiguity function, Autocorrelation, and Cross-correlation.Waveform shaping-Wikipedia

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Switching Between Diversity and Multiplexing

Wireless communication systems work better when the transmitter can respond to changes in the propagation channel. In a system with a single transmit and receive antenna this often means adjusting the rate or the power of the transmitted signal. In a multi-antenna system it is also possible to adjust the spatial mode. In particular, it is possible to switch between diversity modes (sending a single reliable data stream) and multiplexing modes (sending multiple streams for higher data rates). We were among the first to recognize the importance of switching between diversity and multiplexing modes of operation.

The main idea is as follows. In the late 1990’s there were two competing approaches to communication in a MIMO wireless channel. The first was known as transmit diversity or space-time coding. The idea here was to send redundant information across all the transmit antennas to improve the quality in the received signal. This is a diversity scheme because it exploits the diversity of possible transmission paths between transmitter and receiver to improve reliability. The other scheme proposed for MIMO communication was called spatial multiplexing. The idea in spatial multiplexing is to send an independent data stream on each antenna thereby effectively sending multiple data streams in parallel. This approach allows the communication system to transmit data generally at a higher rate but typically less reliably than with transmit diversity. In our early work, we proposed the simple idea of switching between transmit diversity and spatial multiplexing based on the channel state. This has the benefits of both reliable signal transmission and high data rates.

In the past several years we have enhanced the concept of switching between diversity and multiplexing in a number of ways. For example, we combined this approach with limited feedback. The ideas is to dynamically adjust the number of transmitted streams based on the channel. When the channel could support only one stream, the transmitter would use beamforming and the receiver would indicate which beamforming vector to use via the limited feedback beamforming framework I developed. When the channel could support additional modes, this would be signaled to the transmitter along with appropriate limited feedback information. This work, called multi-mode precoding, allows the communication link to operate near the theoretical link capacity while at the same time only requires low receiver processing complexity. In later work we investigated the idea of switching between diversity and multiplexing based on spatial correlation information. This has the advantage of reducing the amount of overhead signaling required since the correlation of the channel varies more slowly than the channel itself.

Select Publications

C. B. Chae, A. Forenza, R. W. Heath, Jr., M. R. McKay, and I. B. Collings, “Adaptive MIMO Transmission Techniques for Broadband Wireless Communication Systems,” IEEE Communications Magazine, May 2010, pp. 112-118.

This paper reviews a framework for MIMO adaptation based on choosing the spatial mode on spatial correlation information, while choosing the rate based on instantaneous channel state information. In this way, the number of data streams varies more slowly than the rate on the streams. The paper is based in part on a tutorial given at several major conferences.

H. Kim, C. B. Chae, G. de Veciana, and R. W. Heath, Jr., “A Cross-Layer Approach to Energy Efficiency for Adaptive MIMO Systems Exploiting Spare Capacity,” IEEE Trans. on Wireless, vol. 8, no. 8, pp. 4264-4275, August 2009.

This is recent work that proposes to switch between MIMO and SIMO modes of operation, on the uplink, to save RF energy, including circuit power in the optimization. The motivation is that multiple transmit antenna RF chains consume more power than a single chain. When the system is lightly loaded (has spare capacity) it is good to send to users at potentially lower rates to save energy.

A. Forenza, M. R. McKay, A. Pandharipande, R. W. Heath, Jr., and I. B. Collings, “Adaptive MIMO Transmission for Exploiting the Capacity of Spatially Correlated Channels,” IEEE Trans. on Veh. Tech., vol. 56, no. 2, pp. 619-630, March 2007.

This paper proposes spatial mode adaptation based on spatial correlation. The idea is to show how different transmission strategies like space-time block coding, hybrid transmission, and spatial multiplexing, all have a different dependence on the transmit spatial correlation matrix. Depending on the eigenvalues of the spatial correlation matrix, switching points can be derived as a function of SNR that show when different transmission techniques are optimum.

M. R. McKay, I. B. Collings, A. Forenza, R. W. Heath, Jr., “Multiplexing / Beamforming Switching for Coded-MIMO in Spatially-Correlated Rayleigh Channels,” IEEE Trans. on Veh. Tech., vol. 56, no. 5, part 1, pp. 2555-2567, Sept. 2007.

This paper derives criteria for switching between diversity and multiplexing in systems that employ bit interleaved coded modulations. Of particular interest, this paper uses various accurate approximations for the coded bit error rate to derive the switching points.

N. Khaled, B. Mondal, R. W. Heath, Jr., G. Leus, and F. Petre, “Interpolation- Based Multi-Mode Precoding for MIMO-OFDM Systems with Limited Feedback,” IEEE Trans. on Wireless, vol. 6., no. 3, pp. 1003-1013, March 2007.

In this paper we established the concept of multi-mode precoding for MIMO-OFDM systems. The idea is to send back quantized versions of the right singular vectors and the preferred modes separately. Then the right singular vectors can be interpolated at the transmitter followed by mode selection. The proposed approach gives very good error rate performance with little feedback overhead.

D. J. Love and R. W. Heath, Jr., “Multimode Precoding for MIMO Wireless Systems,” IEEE Trans. on Signal Processing, vol. 53, no. 10, part 1, pp. 3674 – 3687, October 2005.

Here we the concept of multi-mode limited feedback precoding. The idea is to have multiple limited feedback precoding codebooks, each for a different number of modes (one-stream, two-stream, etc). Suboptimum selection algorithms were proposed to enable selecting the number of spatial modes first, followed by the appropriate codeword index.

R. W. Heath, Jr. and D. J. Love, “Multi-Mode Antenna Selection for Spatial Multiplexing with Linear Receivers,” IEEE Trans. on Signal Processing, vol. 53, no. 8, part 2, pp. 3042-3056, August 2005.

This paper introduces the concept of multi-mode antenna selection. The idea is to use antenna subset selection as a form of limited feedback precoding. The number of spatial modes, and the mapping of streams to antenna, are communicated from the receiver to the transmitter via a low rate feedback link. This paper shows that it is possible to achieve full diversity and near capacity performance with just N bits of feedback where N is the number of transmit antennas.

R. W. Heath, Jr. and A. J. Paulraj, “Switching Between Diversity and Multiplexing in MIMO Systems,” IEEE Trans. on Communications, vol. 53, no. 6, pp. 962-968, June 2005.

This is the original paper on switching between multiplexing and diversity. Don’t be deceived by the date, the original manuscript was submitted in 2001. The idea here is to switch between spatial multiplexing (2 streams) and space-time block coding (1 stream) with only a single bit of feedback. Some analysis of switching thresholds is provided, motivating the use of the Demmel condition number as a metric for MIMO channel quality.

S. Catreux, V. Erceg, D. Gesbert, and R. W. Heath, Jr., “Adaptive Modulation and MIMO Coding for Broadband Wireless Data Networks,” IEEE Communications Magazine, pp.108-115, June 2002.

This paper describes the key ideas behind the link adaptation algorithm developed at Iospan Wireless for one of the first MIMO-OFDM wireless systems. The insight was that the mean and variance of the post-processing SNR in the frequency domain could be used to build lookup tables for choosing between diversity and multiplexing with different amounts of spatial and frequency selectivity. Realistic system level simulations show that MIMO provides spectral efficiency improvements even in interference limited cellular systems.

Awards

Received the best student paper award (given to A. Forenza and M. R. McKay) for the paper:

Transmit Diversity Vs Spatial Multiplexing

A. Forenza, M. R. McKay, R. W. Heath, Jr., and I. B. Collings, “Switching between OSTBC and spatial multiplexing with linear receivers in spatially correlated MIMO channels,” Proc. of the IEEE Vehic. Tech. Conference, vol. 3, pp. 1387-1391, Melbourne, Australia, 7-10 May 2006.

Transmit Diversity And Receive Diversity

Sponsors

Transmit Diversity Vs Spatial Multiplexing

We have been fortunate to have several sponsors of our work including the Office of Naval Research and the National Science Foundation. We have also had several industrial sponsors in the past including Motorola, Samsung, and Freescale. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of any sponsors of this work.