Apparatus, system and method for providing a multiple input/multiple output (MIMO) channel interface

A system, method and apparatus, provide for the utilization of the MIMO technique with single-antenna communication devices that maximize high-speed broadband communication. The apparatus includes a wireless communication interface (WCI) device configured to exchange wireless signals with a base station through a multiple input multiple output (MIMO) air interface and to exchange a corresponding set of wireless signals with an access terminal through a wideband air interface having a greater bandwidth than the bandwidth of the MIMO air interface. The system includes a plurality of WCI devices communicating with the base station and exchanging corresponding signals with the access terminal.

FIELD OF THE INVENTION

The invention relates in general to wireless communication devices and more specifically to a device, system and method for providing a MIMO channel interface.

BACKGROUND OF THE INVENTION

A recently developed technology known as multiple-input/multiple output (MIMO) is emerging as a key technology enabler for high-speed broadband communications. This technology is especially useful for communication channels that are bandwidth and power-limited. It relies on the use of multiple transmit and receiver antennas to achieve very large capacity gains compared to single transmit/receive antenna systems.

It has been shown that extremely high spectral efficiencies can be achieved without bandwidth expansion when the communication channel has sufficiently rich scattering characteristics and the antennas at both transmit and receive ends are separated by sufficient distances. A feature of MIMO technique is that MIMO processing effectively creates multiple independent parallel communication channels within the same frequency band by using multiple transmit and receive antennas and exploiting the scattering characteristics of the transmission medium. Studies and experiments have shown that capacity gains from MIMO techniques depend heavily on the channel gain correlations at the different receive antennas as well as the ability to estimate those gains accurately. Typically, a separation between antenna elements on the order of several wavelengths is required to provide sufficient decorelation between channel gains. This is especially problematic in the case of handheld devices and other devices whose physical dimensions limit the number and separation of multiple receive antenna elements.

Accordingly, there is a need for a device, system and method that provide for the utilization of MIMO communication systems with single-antenna communication devices.

SUMMARY OF THE INVENTION

A system, method and apparatus, provides an interface between a MIMO communication system and single-antenna communication devices. The apparatus includes a wireless communication interface (WCI) device configured to exchange wireless signals with a base station through a multiple input multiple output (MIMO) air interface and to exchange a corresponding set of wireless signals with an access terminal through a wideband air interface having a greater bandwidth than the bandwidth of the MIMO air interface. A downlink transceiver is configured to transmit wideband downlink signals to the access terminal corresponding to downlink MIMO signals received from the base station through the MIMO air-interface. In the exemplary embodiment, the apparatus includes a second transceiver configured to transmit uplink MIMO signals to the base station corresponding to uplink wideband signals received from the access terminal. The system includes a plurality of WCI devices communicating with the base station and exchanging corresponding signals with the access terminal. Each wireless communication interface device is configured to measure channel characteristics between each WCI device and the base station transmit antennas and to send channel state information corresponding to the channel characteristics to the base station. Based on the channel state information, the MIMO base station precodes the downlink MIMO signals allowing the WCI to receive and process the downlink signals independently.

DETAILED DESCRIPTION

In the exemplary embodiment, at least two WCI devices are geographically distributed within a communication range of a base station. Each WCI device exchanges wireless signals with the base station through a MIMO air interface. Each WCI device receives wireless downlink MIMO signals transmitted from multiple antennas of the base station, such as an access node, through a MIMO frequency bandwidth. The WCI devices demodulate and decode the downlink MIMO signals. The resulting signals are coded, modulated and transmitted through a wideband air interface such as an ultra wideband (UWB) communication channel that has a wider frequency bandwidth than the MIMO frequency bandwidth. The access terminal receives and processes the downlink wideband signals transmitted from the WCI devices to recover the information transmitted by the base station. The WCI devices demodulate and decode uplink wideband signals transmitted from the access terminal and transmit corresponding uplink MIMO signals to the base station.

FIG. 1is a block diagram of wireless communication network100in accordance with an exemplary embodiment of the invention. An arrangement of wireless communication interface (WCI) devices102forming a wireless communication interface system103can communicate with at least one base station (BS)104and at least one access terminal106. Although the base station104is stationary in the exemplary embodiment, the base station104may be a mobile unit in some circumstances. The access terminal106may be a single-antenna device such as a cellular telephone, wireless modem, personal digital assistant (PDA) or other device that exchanges electromagnetic signals with a fixed or portable communication device. In the exemplary embodiment, the access terminal106includes hardware, software, and firmware not shown inFIG. 1for facilitating and performing the functions of the access terminal106. For example, the access terminal106includes input and output devices such as keypads, displays, microphones and speakers. As described in further detail below, the BS104includes an arrangement of antennas108in order to support multiple-input/multiple output (MIMO) communication with the WCI devices102in the exemplary embodiment, The WCI devices102each include at least one antenna109for transmitting and receiving signals with the base station104and at least another antenna119for exchanging signals with the access terminal106. In some situations, a single antenna may be used. Further, multiple antennas may be used to facilitate communication through the MIMO air interface. AlthoughFIG. 1shows two WCI devices102providing communication services to two access terminals106, any number of WCI devices102may provide services to any number of access terminals106.

A communication channel illustrated as a MIMO air-interface110provides a medium where downlink MIMO signals112and uplink MIMO signals113are exchanged between the BS104and each of the WCI devices102. The communication channel may include buildings, automobiles, and other objects that cause the deflection of the communication signals and result in a rich scattering of the communication signals. In the exemplary embodiment, MIMO signals112,113are exchanged through the MIMO air-interface110within a MIMO frequency bandwidth such as a narrowband (NB) frequency bandwidth. The MIMO signals may be transmitted in accordance with any of several communication or modulation techniques. MIMO processing is a key aspect of most upcoming wireless systems, including next generation cdma2000 systems (e.g. EV-DO Phase 2), next generation WCDMA systems (e.g. WCDMA Long Term Evolution (LTE)), wireless local area network (WLAN) systems such as IEEE 802.11 (first introduced in 802.11n), WiMAX (mobility enhancements in IEEE 802.11e) and Mobile Broadband Wireless Access (IEEE 802.20).

The downlink MIMO signals112received by each WCI device102are processed and retransmitted as downlink wideband signals114through the wideband air interface118to the access terminal106. The bandwidth of the wideband air interface118is greater than the MIMO frequency bandwidth. In the exemplary embodiment, the wideband air interface118is an interface in accordance with any communication scheme characterized as ultra wideband (UWB). Examples of suitable modulation and access techniques for the wideband air interface118include orthogonal frequency division multiple access (OFDMA) schemes and direct sequence techniques such as code division multiple access (CDMA). In the exemplary embodiment, the wideband air interface118provides for short-range, low-power, high-data rate communication that can be utilized with single-antenna user devices. Accordingly, communications through the wideband air interface typically have lower spectral densities than communication over the MIMO channel.

Uplink wideband signals115are transmitted by the access terminal106using different channels of the wideband air interface. The WCI devices102receive the uplink wideband signals115and transmit corresponding uplink MIMO signals113to the base station104through the MIMO air interface.

Accordingly, the exemplary embodiment provides for the implementation of a plurality of WCI devices102that enable high-speed broadband communication between at least one single-antenna access terminal106and a MIMO BS104. The use of short-range, low-power, and high-data rate feature of the UWB technology can provide for high-speed broadband communication with the access terminal106for effectively utilizing MIMO technology in locations where a system103of WCI devices102can be installed in close proximity to the access terminal106. For example, the system103of WCI devices102can be installed around the house of a user allowing for a high-speed broadband communication between the access terminal106and the BS104through the system of WCI devices102. Examples of other suitable locations for installing the system103of WCI devices102includes shopping malls, airports, train stations, buses, cars or other locations where there are high levels of human traffic and the user devices are in close proximity to the WCI devices102. Therefore, by combining the strengths of the NB MIMO and UWB communication, the exemplary embodiment provides for high-speed broadband communication between a single-antenna access terminal106and a base station104communicating using MIMO techniques. The exemplary system provides a method for trading off spectrum bandwidth and space since the MIMO channel and the UWB channel support the same overall data rate (or channel capacity). However, the MIMO channel achieves a high data rate by spatially multiplexing multiple conventional single-input single output channels, thus achieving very high spectral efficiency (bits/s/Hz). The UWB channel achieves a high data rate by using a very large spectrum bandwidth. The system has the additional advantage that the estimation of the MIMO channel parameters required at the receiver or transmitter is simplified compared to the case where the multi-antenna system is part of the access terminal, since the WCI devices will typically be stationary or following a predictable path (e.g. located on a train or plane) whereas the access terminal might not. Another advantage is that the estimation of the MIMO channel parameters is performed by the BS and the WCI devices, not the access terminals. Thus, in a multi-access configuration, the channel estimation task does not need to be performed on a per access terminal basis.

As explained above, the MIMO technique requires multiple antennas on a device separated by a distance of several wavelengths. Most user devices are single-antenna devices or if they are multiple-antenna devices, the antennas are not separated by several wavelengths. Such user devices may not operate and communicate in a MIMO communication environment. Conventional access terminals cannot benefit from the advantages of conventional MIMO communication. The exemplary embodiment provides a technique for realizing those advantages. The exemplary communication system may be viewed as a distributed antenna and transceiver network that is wirelessly connected to the access terminal106. Since each WCI device102includes at least one antenna and a transceiver, the MIMO signals may be processed with the advantage of separated antennas to fully utilize the MIMO environment. The information is forwarded to the access terminal106using a short distance, low power, air interface that can easily be processed with single antenna.

In the exemplary embodiment, the WCI devices102operate independently. Processing in conventional MIMO receivers requires information received from multiple antennas to be processed as an aggregate set of information. In the exemplary embodiment, however, the transmitted downlink MIMO signals112are precoded at the base station104based on channel characterizations obtained from the WCI devices102. By precoding the transmissions, each WCI device102can independently process the incoming downlink MIMO signals112and forward the information to the access terminal106as if the WCI devices102were operating as a single unit. Precoding at the base station104is discussed in further detail below.

FIG. 2is a block diagram representation of the WCI device102in accordance with the exemplary embodiment of the invention. The functions and operations of the blocks described inFIG. 2may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device and the functions described as performed in any single device may be implemented over several devices. For example, software running on a processor within the WCI device102may perform at least some of the functions of the demodulators208,218and the modulators210,220.

The WCI device102includes at least one transceiver204,214that can receive and transmit MIMO and wideband signals. In the exemplary embodiment, the WCI device102includes a downlink transceiver204and an uplink transceiver214. The downlink transceiver204receives downlink MIMO signals112from the MIMO base station104through the MIMO antenna109and transmits corresponding downlink wideband signals114to the access terminal106through the other antenna119. The uplink transceiver214receives uplink wideband signals115from the access terminal106through the wideband antenna119and transmits corresponding uplink MIMO signals113to the MIMO base station104through the MIMO antenna109. The antennas109and119are connected to the downlink transceiver204and uplink transceiver214through associated duplexers226and228. The downlink transceiver204includes a narrow band receiver209and a wideband transmitter213and the uplink transceiver214includes a wideband receiver219and a narrow band transmitter223. A downconverter206in the NB receiver209frequency shifts the incoming downlink MIMO signal to baseband. The NB demodulator208demodulates the baseband signal to recover the transmitted data symbols. The data is forwarded to the wideband modulator210in the wideband transmitter213where it is modulated in accordance with the appropriate wideband modulation technique. An upconverter212frequency shifts the modulated signal to the RF signal for transmission to the access terminal106. The downlink wideband signals are transmitted through the duplexer228and the wideband antenna119to access terminal106. In some circumstances, the functions of the wideband transmitter213may include spreading the baseband signal with a PN code such as in direct sequence spread spectrum techniques.

A downconverter216in the wideband receiver219frequency shifts the uplink wideband signal115transmitted from the access terminal106and received through the wideband antenna119from RF to baseband. The wideband demodulator218demodulates the baseband signal to receive the data symbols. The data is modulated by the narrow band modulator220, frequency shifted by the upconverter222to RF signals and transmitted to the base station104through the MIMO antenna109. In some circumstances, the wideband receiver219applies a PN code to despread the incoming uplink wideband signal. The RF signals are uplink MIMO signals having, for example, a narrow band bandwidth that are transmitted through the duplexer226and MIMO antenna109to base station104.

Accordingly, in the exemplary embodiment, downlink MIMO signals112are received by each of the WCI devices102from the base station104and converted to downlink wideband signals114and further transmitted to the access terminal106. Also, the uplink wideband signals115received from the access terminal106by each of the WCI devices102are converted to uplink MIMO signals113and further transmitted to the base station104.

In the exemplary embodiment, the WCI device102also includes a channel processor224that is connected to the NB receiver209for monitoring the downlink MIMO signals112from the base station104. The channel processor224is configured to measure the channel characteristics between the WCI device102and the transmission antennas108of the base station104. Examples of parameters that may be monitored include signal strength, signal phase, and delays between multiple signal versions of downlink MIMO signals112. The channel processor224determines channel state information (CSI) from the channel characteristics and communicates the CSI to the NB modulator220of the uplink transceiver214through which the CSI is transmitted to the base station104. The CSI may include raw data measurements in some circumstances. Transmitting the CSI to the base station104allows the base station104to perform at least some of the MIMO processing normally performed by a conventional MIMO receiver. The base station104precodes signals to compensate for the channel characteristics allowing the WCI devices102receive signals without information from other WCI devices102. Accordingly, each WCI device102can operate independently from other WCI devices102.

FIG. 3is a block diagram representation of a base station104in accordance with the exemplary embodiment of the invention. The functions and operations of the blocks described inFIG. 3may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device and the functions described as performed in any single device may be implemented over several devices.

A MIMO precoder304in the base station104processes the data in accordance with a precoding scheme based on the channel characteristics associated with each WCI device102. In the exemplary embodiment, outgoing data is processed by a rateless encoder318before precoding in the MIMO precoder304. The rateless encoder318provides a mechanism to more securely transmit information and is shown as a dashed line block to illustrate that the rateless encoder318may not be used in some implementations. Rateless coding has been shown to be very effective when multiple unreliable channels exist between a transmitter and a receiver, and has been proposed for the transmission of broadcast and multicast information over the Internet. MIMO communication can be viewed as a method to provide a number of parallel, independent communication channels corresponding to the different eigenvectors of the MIMO channel. In a Rayleigh fading environment, the MIMO channel can be described by a matrix of complex, zero-mean, Gaussian, independent random variables, and as a result, each of the eigenmodes undergoes fading. Rateless coding is ideally suited for MIMO communication because it inherently exploits the existence of multiple paths between transmitter and receiver, to achieve high reliability with little overhead.

Since multiple signals are transmitted through multiple channels to multiple WCI devices102, the operations of the MIMO precoder are matrix operations. Precoding is a transmitter-side equalization technique that is the counterpart of the better-known receiver-side decision feedback equalization technique. Analogous to decision feedback equalization, it generally consists of two parts, a feedforward portion and a feedback portion. The feedforward and feedback parts can be designed according to a variety of criteria. For example, the feedforward and feedback parts may be chosen such that the overall effect of feedforward, feedback and channel processing make the MIMO channel appear as a set of M independent, unit-gain channels (where M is the number of receive devices). In this case, the feedforward part is designed such that the combination of feedforward processing with the MIMO channel matrix results is a lower triangular matrix. This makes it possible for the feedback part to successively cancel the remaining interference in the case of decision feedback equalization, or to successively pre-equalize the different signals for the different transmit antennas in the case of transmit-side precoding. Another criterion, which leads to another choice of the feedforward and feedback parts, is to minimize the overall effect of the MIMO channel and receiver noise. When precoding includes a modulo device, it is referred to, by those skilled in the art, as Tomlinson-Harashima precoding. The purpose of this modulo device is to reduce the total transmit power without affecting the other properties of the transmitted signals, e.g. the fact that when transformed by the MIMO channel, the outputs appear as M independent, unit-gain communication channels. In the exemplary embodiment ofFIG. 3, the data to be transmitted is combined through a summer316with an output of a feedback matrix unit308and forwarded to a modulo device306. The output of the modulo device306is forwarded to a feedforward matrix unit310and the feedback matrix unit308. The matrix devices308and310together with the vector modulo device306and vector summer316implement Tomlinson-Harashima precoding and provide the appropriate processing to allow independent receiver-side demodulation and decoding in each of the WCI units. Channel state information is received by down-converting and demodulating the incoming signals in a downconverter320and demodulator320. Based on the channel state information received from the WCI devices102, a channel state information processor317determines the appropriate parameters of the matrix units308,310. The CSI processor317provides appropriate values to the matrix units308,310to correspondingly change the values in each matrix unit such that output signals from the feedforward matrix unit310are appropriately transformed and compensate for the channel conditions with each WCI device102. Therefore, each WCI device102receives pre-coded data from the base station104that enables each WCI device102to independently exchange signals between the base station104and the access terminal106. The precoded signals are frequency shifted by an upconverter314before transmission by a transceiver302through the appropriate antenna108.

FIG. 4is a block diagram of an access terminal106in accordance with the exemplary embodiment of the invention. Wideband signals are transmitted and received through an antenna401. A transceiver400includes a duplexer402coupled to the antenna401, and a wideband receiver404, a NB receiver406, a NB transmitter412, and a wideband transmitter414. In some circumstances, the access terminal106of the exemplary embodiment may comprise a rateless decoder408and a rateless encoder410(shown as dashed line blocks). In the exemplary embodiment, the access terminal106through the wideband receiver404receives from the plurality of WCI devices102a plurality of downlink wideband signals114corresponding to a plurality of downlink MIMO signals112. The wideband receiver404is configured to separate the received downlink wideband signals114and generate corresponding baseband (BB) signals405. Since several WCI devices102may be communicating with the access terminal106at the same time, different received downlink wideband signals114can be distinguished from one another using techniques such as frequency-hopping or spreading with a pseudo noise PN code. The NB receiver406is connected to the wideband receiver404for receiving the baseband signals and processing the baseband signals to recover information. It should be noted that the NB receiver406may include a NB processor and a multiplexer (not shown) that can process and multiplex the received BB signals and provide a resultant signal in the form of a high data rate signal407which can be decoded by the access terminal106. As explained above, the exemplary embodiment access terminal106may include the rateless decoder408if the base station104transmits rateless encoded downlink MIMO signals112. In that situation the high data rate signal407may be decoded by the rateless decoder408.

For uplink communication with the WCI devices102, the transceiver400of the access terminal106may utilize the rateless encoder410for encoding the uplink signals. The NB transmitter412generates a plurality of uplink communication signals corresponding to NB signals. The wideband transmitter414connected to the NB transmitter412is configured to transmit different uplink wideband signals115corresponding to the uplink communication signals received from the NB transmitter412. The access terminal106is further configured to transmit a different uplink wideband signal115to each of the WCI devices102simultaneously. Techniques such as frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA) and orthogonal spreading format can be employed for transmitting the different uplink wideband signals115to the WCI devices102. In the exemplary embodiment, the access terminal106includes hardware, software, and firmware not shown inFIG. 4for facilitating and performing the functions of the access terminal106. For example, the access terminal106may include user interface devices such as a display, microphone, speaker, and keyboard.

Therefore, information originally transmitted by the MIMO base station104is received by the WCI devices102and transmitted to the access terminal106through multiple channels of a wideband frequency spectrum. The wideband signals114are demodulated to recover the original MIMO signals that are decoded by the narrowband receiver406and multiplexed to produce the high data rate signal407. For example, where the wideband air interface118is a CDMA air interface, a WCI device102transmits a received narrow band MIMO signal as a spread spectrum, low power, low spectral density signal over a CDMA channel. Other WCI devices102transmit their received MIMO signals on other CDMA channels. The access terminal106receives the multiple CDMA channels using a CDMA receiver and the narrowband receiver406processes the resulting narrow band signals to receive the original MIMO high data rate signal.

In the exemplary embodiment ofFIG. 1, multiple access terminals106share the set of WCI devices102. It is desirable that all the access terminals be able to communicate with all the WCI devices to achieve the highest peak throughput to each user. However, this is not always possible, since some of the access terminals may only be able to communicate with a subset of the WCI devices. In this case, the BS may be instructed through signaling to adapt its MIMO processing to the set of access terminals being served at that point in time and frequency. For example, the base station104may choose to code the signals for a subset of the WCI devices, or it may choose to use the remaining set of WCI devices to communicate with other access terminals.

In addition to exploiting the advantages of MIMO techniques and wideband communication such as UWB, the exemplary system provides other operational advantages. When signals are received by any access terminal106, the access terminal106can decode a subset or decode all of the signals and be able to decode the initial data stream, thereby trading off channel capacity for delay without requiring additional retransmissions such as automatic request (ARQ) from the BS104. The preceding situation may occur, for example, when one or more of the WCI devices102experience poor channel conditions in connection with access terminal106.

FIG. 5is a flow chart of a method performed in the WCI device in accordance with the exemplary embodiment. The method can be executed using any combination of hardware, software and/or firmware.

At step502, the downlink MIMO signals112from the base station104are received by the WCI device102through the MIMO air interface110having a MIMO bandwidth. In the exemplary embodiment, the narrow band receiver209in the downlink transceiver204downconverts and demodulates the narrow band signals transmitted from the base station104. The narrow band receiver209performs a portion of the functions typically performed by a conventional MIMO receiver since the WCI device102includes a single antenna for receiving the downlink MIMO signals112.

At step504, the downlink wideband signal114corresponding to the downlink MIMO signal112is transmitted to the access terminal106through the wideband air interface118having a bandwidth greater than the MIMO bandwidth. In the exemplary embodiment, the baseband signals recovered by the narrowband receiver209are modulated and upconverted by a wideband transmitter213in the downlink transceiver204. The resulting downlink wideband signals114are transmitted to the access terminal106through the wideband air interface118.

At step506, the uplink wideband signals115are received from the access terminal106through the wideband air interface118. In the exemplary embodiment, the wideband receiver219in the uplink transceiver214downconverts and demodulates the uplink wideband signals115transmitted from the access terminal106. The uplink wideband signals115are transmitted through the wideband air interface118over multiple channels. The wideband signals115may be transmitted by the access terminal106in accordance with CDMA techniques where several narrowband signals are transmitted on different direct sequence channels that are demodulated by the wideband receiver219of the WCI device102to receive the narrowband signals.

At step508, the uplink MIMO signal113corresponding to the uplink wideband signal115is transmitted to the base station104through the MIMO air interface110. In the exemplary embodiment, the narrowband baseband signals recovered by the wideband receiver219are modulated and upconverted by the narrowband transmitter223. The resulting signals are transmitted through the MIMO air interface110to the base station104. Since multiple WCI devices transmit the narrowband signals from different geographical locations, the resulting combination of signals received at the base station antennas108is in accordance with MIMO transmission allowing the MIMO base station104to recover the originally transmitted high data rate signal that was separated onto the different wideband signals.

Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.