Multiple antenna system for varying transmission streams

MULTIPLE ANTENNA SYSTEM FOR VARYING TRANSMISSION STREAMS

BACKGROUND OF THE INVENTION [0001] I. Field of the Invention

[0002] The present invention relates to wireless communications, and more particularly to a multiple antenna system.

[0003] II. Description of the Related Art

[0004] It has been observed that traditional MultipleInput, Multiple-Output ("MIMO") antenna systems do not optimally perform when channel characteristics for each individual transmission path are relatively different. This non-optimal performance has been measured by packet error rates and system throughput. Presently, these MIMO antenna systems transmit equal amount of bits on each antenna using the same modulation, irrespective of different capacities of each of the channels in the system. One known approach utilizes aggregate capacity information of the MIMO antenna system—or the equivalent thereof—for determining a suitable modulation and information rate to be used for each transmit antenna. For the purposes of the present disclosure, information rate may be defined as the number of information bits that can be transmitted using a particular transmission path over a given amount of time.

[0005] While using aggregate capacity information provides for a number of performance improvements, it is not ideal. Fundamentally, the aggregate capacity of each of the channels in the MIMO antenna system may not reflect the channel condition and capacity that each transmit antenna can support. Consequently, a need exists for a MIMO antenna system reflecting the channel condition and capacity that each transmit antenna may support.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method for varying at least one transmission stream of plurality in response to the condition of the channel over which the varied transmission stream may be transmitted. For the purposes of the present invention, a plurality of transmission streams may be formed from a number of packets and/or bits derived from an information stream, wherein each transmission stream may comprise data, bits, symbols and/or packets.

[0007] In an embodiment of the present invention, the modulation of each transmission stream may be varied. Each transmission stream is loaded onto a transmission path having at least one antenna. Each transmission path also may comprise a modulator for varying the corresponding transmission stream in accordance with the condition of the channel of that transmission path. The condition of each channel may be ascertained from determining the air interface characteristics of the antenna corresponding with that channel of the particular transmission path.

[0008] In another embodiment of the present invention, the rate of each transmission stream may be varied. For the purposes of the present invention, rate matching may be defined as matching an information rate of a transmission path to the air interface characteristics of that transmission path by filling in one or more bits into the corresponding transmission stream and/or puncturing out one or more bits

from the corresponding transmission stream. Each transmission stream is loaded onto a transmission path having at least one antenna. Each transmission path also may comprise a rate matching device for varying the corresponding transmission stream in accordance with the condition of the channel of that transmission path. The condition of each channel may be ascertained from determining the air interface characteristics of the antenna corresponding with that channel of the particular transmission path. In one example, each rate matching device may puncture at least one bit from the relevant transmission stream and/or fill the transmission stream with at least one bit. By puncturing and/or filling, the size of each transmission stream, consequently, may be controlled, and thusly, the capacity of each channel may be maintained and/or desirably modified.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

[0010] FIG. 1 depicts known multiple antenna system;

[0011] FIG. 2 depicts an embodiment of the present invention;

[0012] FIG. 3 depicts another embodiment of the present invention; and

[0013] FIG. 4 depicts another embodiment of the present invention.

[0014] It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations, and thus are not intended to portray the specific dimensions of the invention, which may be determined by skilled artisans through examination of the disclosure herein.

DETAILED DESCRIPTION

[0015] As detailed hereinabove, various multiple-input, multiple-output ("MIMO") antenna systems are known. One known MIMO antenna system 10 is illustrated in FIG. 1. MIMO antenna system 10 receives data blocks 12 as an input. More particularly, system 10 includes a device 15 for receiving data blocks 12. Device 15 converts each received data block into at least one information stream 18. An information stream, for the purposes of the present invention, may be defined as a number of packet and/or bits derived from an initial block of data.

[0016] System 10 self-determines its aggregate capacity. More particularly, system 10 determines the collective air interface characteristics 22 of transmit antennas, 401; 402 through 40;. This determination may be achieved by various means known in the art. In one approach, the capacity of the collective transmit antennas is determined using a test signal transmitted from system 10 to a wireless user and retransmitted back to system 10. From this exchange, aggregate air interface characteristics 22 of system 10 may be ascertained.

[0017] Thereafter, the size of each information stream may be modified to maintain the aggregate capacity of system 10 at a steady state. To this end, multiple antenna system 10 includes a device 20 for performing rate matching in response to the established aggregate air interface characteristics 22 of system 10. Device 20 receives each information stream 18, one at a time. As a result, device 20 may puncture one or more bits from each stream. Alternatively, device 20 may fill each information stream 18 with one or more additional bits. By puncturing or filling each information stream 18, the size of each information stream, consequently, may be controlled, and thusly, the aggregate capacity of system 10 may be maintained.

[0018] Once rate matched, each information stream is processed by a modulator 25. Modulator 25 modulates the contents of each information stream. More particularly, modulator 25 generates symbols from each information stream encoded according a scheme selected in response to aggregate air interface characteristics 22 of system 10. Consequently, the symbols generated from an information stream by modulator 25 may vary in accordance with the determined aggregate capacity of system 10.

[0019] The symbols generated by modulator 25 are correspondingly fed into a demultiplexer 30. Demultiplexer 30 distributes the generated symbols for each information stream equally amongst each transmission path, 351; 352 through 35;. Thusly, transmission paths, 35x, 352 through 35;, each receive an equal number of symbols, which are directed to a corresponding transmit antenna, 40-;, 402 through 40;, for subsequent transmission. For the purposes of the present invention, the parceling of the information stream amongst transmission paths, 351; 352 through 35;, creates a number of transmission streams corresponding with the number of paths. In the illustrated example of FIG. 1, each transmission stream comprises a group of transmission symbols. It will be apparent to skilled artisans, however, that each transmission stream may merely comprises a number of packets and/or bits derived from an information stream.

[0020] It is becoming increasing apparent that for certain applications MIMO antenna system 10 of FIG. 1 may not offer optimal performance when channel characteristics for each individual transmission path are relatively different. System 10 may not support the most advantageous MIMO operation, as measure by packet error rates and/or throughput. This non-optimal performance may be attributed to the recognition that the capacities of each of the channels associated with system 10 may differ from channel to channel. More particularly, rate matching device 20 rate matches the information stream and/or modulator 25 modulates the information stream each in response to the aggregate capacity of the entire system 10. Thusly, neither rate matching device 20 nor modulator 25 considers the individual capacity of each channel of the entire system 10. By exclusively considering the aggregate capacity to determine the suitable rate matching and/or modulation employed, the packet error rate and/or throughput of system 10 may not operate optimally.

[0021] To overcome the limitations of system 10 of FIG. 1, the present invention varies one or more transmission streams to be loaded onto one or more antennas. More particularly, each transmission stream may be modified in response to the individual capacity of that transmission stream's associated antenna. In considering the individual capacities of each channel, the present invention may also vary the Walsh code employed in conjunction with each

transmission stream. Moreover, the present invention enables the transmit time interval ("TTI") of each transmission stream to be varied in accordance with the individual capacity of each channel.

[0022] Referring to FIG. 2, a first embodiment of the present invention is illustrated. More particularly, a MIMO antenna system 100 is depicted for varying at least one transmission stream in response to the individual capacity of that transmission stream's associated antenna. System 100 includes a device 110 for receiving data blocks 112. Device 110 converts each received data block into at least one information stream 115. In one example, device 110 comprises a cyclic redundancy checker.

[0023] To vary at least one transmission stream in response to the individual capacity of that transmission stream's associated antenna, the condition of each of channel needs to be determined. The condition and capacity of each channel may be ascertained from the individual air interface characteristics, 1221, 1222 through 122;, of each transmit antenna, 1401; 1402 through 140;. These individual air interface characteristics, 122-;, 1222 through 122;, may be derived using various techniques, including a feedback mechanism between each transmitting antenna of system 100 and the one or more wireless units interacting with system 100. In single antenna systems, it is known to use a channel quality indicator may be fedback to the transmitting system over a control channel. The channel quality in such system is based on the average received signal-to-noise ratio calculated at a wireless unit. In one example, the air interface characteristics may each be reduced to a vector of propagation coefficients. In another example, the air interface characteristics may be represented by a vector of received signal-to-noise ratios for each transmission path.

[0024] Each information stream 115 is fed into a demultiplexer 120. Demultiplexer 120 demultiplexes each information stream 115 to create a plurality of transmission streams. Demultiplexer 120 supports a plurality of transmission paths, 125-;, 1252 through 125;, by creating the corresponding plurality of transmission streams. Thusly, each transmission path comprises a transmission stream. It should be noted that, in one example, the transmission streams, as demultiplexed from a received information stream, might each comprise an equal number of bits. However, it will be apparent to skilled artisans that demultiplexer 120 may weigh each transmission path differently such that the distribution of demultiplexed bits forms transmission streams of differing bit lengths relative to each other. In the later exemplary scenario, the weighting of each transmission path by demultiplexer 120 and the distribution of demultiplexed bits may be influenced by air interface characteristics of each transmit antenna.

[0025] Once transmission paths, 1251; 1252 through 125;, are defined from information stream 115 by demultiplexer 120, each transmission stream is fed into a corresponding rate matching device, 1301; 1302 through 130;. Each rate matching device may alter the information rate of the transmission stream, in response to the air interface characteristics of the antenna associated therewith. If, for example, the air interface characteristics show a relatively low attenuation pattern, then each rate matching device may fill the corresponding transmission stream with one or more additional bits to enlarge the number of bits to be transmitted and maintain a particular transmission rate. Conversely, should the air interface characteristics show a relatively high attenuation pattern, each rate matching device might puncture one or more bits from the corresponding transmission stream to lessen the number of bits to be transmitted. By puncturing or filling, the size of each transmission stream, consequently, may be controlled, and thusly, the capacity of each channel within system 100 may be maintained and/or desirably modified.

[0026] Once rate matched, each transmission stream is then processed by a corresponding modulator, 1351; 1352 through 135;. Each modulator modulates the contents of the received transmission stream. More particularly, each modulator generates symbols from each transmission stream encoded according a scheme selected in response to the received air interface characteristics of the antenna corresponding with associated transmission path. Consequently, the symbols generated from any transmission stream may be varied in accordance with the channel condition of the corresponding antenna and that antenna's air interface characteristics. Once rate matched and modulated, the transmission streams associated each transmission path are fed into a corresponding transmit antenna, 1401; 1402 through 140;, for subsequent transmission.

[0027] In one example, the channel condition is represented by the capacity for each transmission path, or equivalently, the number of information bits per second per hertz. Once the capacity for each transmission path is known at the transmitter, the type of modulation scheme may be selected from a pre-determined set of supported modulation schemes in the system. Each modulation scheme converts n bits from a relevant transmission stream into a symbol. After the modulation scheme is selected, the rate matching operation—e.g., the amount of bits to be filled or punctured from the transmission stream—may be determined from the capacity and the type of modulation scheme selected.

[0028] Referring to FIG. 3, another embodiment of the present invention is illustrated. More particularly, a MIMO antenna system 200 is depicted for varying at least one transmission stream in response to the individual capacity of that transmission stream's associated antenna. System 200 includes a device 210 for receiving data blocks 212. Device 210 converts each received data block into at least one information stream 215. In one example, device 210 comprises a cyclic redundancy checker.

[0029] As detailed hereinabove, the condition of each of channel needs to be determined to vary at least one transmission stream in response to the individual capacity of that transmission stream's associated antenna. The condition and capacity of each channel may be ascertained from the individual air interface characteristics, 222x, 2222 through 222;, of each transmit antenna, 245-;, 2452 through 245;. These individual air interface characteristics, 2221; 2222 through 222;, may be derived using various techniques, including a feedback mechanism between each transmitting antenna of system 200 and the one or more wireless units interacting with system 200. In one example, the air interface characteristics may each be reduced to a vector of propagation coefficients. In another example, the air interface characteristics may be represented by a vector of received signal-to-noise ratios for each transmission path.

[0030] Each information stream 215 is fed initially fed into a rate matching device 220. Rate matching device 220

may alter the size of the information stream for subsequent transmission, in response to the air interface characteristics of each antenna in system 200. If, for example, the air interface characteristics of one or more antennas show a relatively low attenuation pattern, then each rate matching device may fill a portion of the information stream, before being converted to an transmission stream, with one or more additional bits to enlarge the number of bits to be transmitted and maintain a particular transmission rate. Conversely, should the air interface characteristics of one or more antennas show a relatively high attenuation pattern, rate matching device 220 might puncture one or more bits from the information stream, before being converted to a transmission stream, to lessen the number of bits to be transmitted. By puncturing or filling the information stream 220, the size of each subsequently formed transmission stream, consequently, may be controlled, and thusly, the capacity of each channel within system 200 may be maintained and/or desirably modified.

[0031] Rate matched information stream 225 is thereafter fed into a demultiplexer 230. Demultiplexer 230 demultiplexes the rate matched information stream to create a plurality of transmission streams. Demultiplexer 230 supports a plurality of transmission paths, 235-;, 2352 through 235;, by creating the corresponding plurality of transmission streams. Thusly, each transmission path comprises a transmission stream. It should be noted that the length of any of the transmission streams, as demultiplexed from a rate matched information stream, might be also varied by demultiplexer 230 in accordance with the air interface characteristics of the corresponding antenna. Consequently, the distribution of bits, for example, between each of the transmission paths may be weighted in an unequal manner as a result of the air interface characteristics of each of the transmit antennas.

[0032] Subsequently, each transmission stream is processed by a corresponding modulator, 240-;, 2402 through 2405;. Each modulator modulates the contents of the received transmission stream, thereby generating encoded symbols. More particularly, each modulator generates symbols from each transmission stream encoded according a scheme selected in response to the received air interface characteristics of the antenna corresponding with associated transmission path. Once modulated, each transmission stream is fed into a corresponding transmit antenna, 2451; 2452 through 245;, for subsequent transmission.

[0033] Referring to FIG. 4, a flow chart depicting one embodiment of the present invention is illustrated. More particularly, a method (300) is depicted for varying one more transmission streams in response to the individual capacity—as determined by the air interface characteristics—of that transmission stream's associated antenna. For the purposes of the present invention, the term stream(s) refers to datum, data, a bit(s), a symbol(s), a packet(s) and/or a combination of data, bits, symbols and/or packet(s).

[0034] Initially, a data block is received and at least one information stream is created (310). The data block may have been processed through a cyclic redundancy checking mechanism. Alternatively, the information stream may be created as a result of performing a cyclic redundancy checking operation.

[0035] Thereafter, the created information stream is demultiplexed into at least two transmission streams (320). Each transmission stream has a transmission path associated therewith. Likewise, a transmit antenna is associated with each transmission path. In one example, the transmission streams may have an equal or unequal number of bits within a given time interval at this point in the method.

[0036] To vary at least one of the transmission streams, the condition and capacity of each channel needs to be ascertained (330). More particularly, the condition and capacity of each channel may be determined from the individual air interface characteristics of that each channel's corresponding transmit antenna. As noted hereinabove, these individual air interface characteristics may be derived using various techniques.

[0037] With the air interface characteristics of each of the channels established, the method then may vary at least one of the transmission streams (340). More particularly, each transmission stream may be varied in response to the air interface characteristics of the corresponding antenna from which it is to be transmitted. This step of varying may comprise modulating and/or rate matching the one or more transmission streams in response to the air interface characteristics of the antenna corresponding with that transmission stream. The step of rate matching may incorporate the steps of puncturing one or more bits from the transmission stream and/or filling the transmission stream with in one or more bits based on the relevant air interface characteristics. It should be noted that the step of varying may also include the step of modifying the transmit time interval ("TTI") in response to the air interface characteristics of the corresponding antenna from which it is to be transmitted. Similarly, the step of varying may further comprise the step of varying Walsh code used with one or more transmission streams in response to the relevant air interface characteristics. As a consequence of these varying steps, the transmission streams may have an equal or unequal number of bits within a given time interval.

[0038] In an example of the present invention, a MIMO antenna system using an M-receive, N-transmit arrangement may be employed in conjunction with the structures and methods detailed hereinabove. After receiving metrics from a receiver, a transmitter computes the modulation and rate for rate matching based on the received metrics. For a given MxN estimated channel matrix

], with each element proportional to the product of Nbps: and Reff;, where Nbps; is the number of bit per symbol dictated by the type of modulation chosen for the ith antenna and R is the effective rate for the ith transmit antenna. The

eff.i

N-tuple vector is then quantized and fedback to the transmitter.

[0041] Thereafter, the transmitter selects the number of Walsh codes (i.e. NWalsh;) available for transmission for the ith antenna as well as the length of the transmission time interval, denoted as TTIsec; for the ith antenna, according to the network resources. It should be noted that the number of Walsh codes does not have to be the same for each antenna. If, however, both NWalsh; and TTIseci are equal for all i=l, . . . , N, the transmitter selects the modulation (e.g., Nbps;) and the effective rate (e.g., Reffi) for each transmit antenna based on C;, the channel condition for the ith transmit antenna. Subsequently, the transmitter computes the number of information bits—an integer multiple of some pre-defined code block sizes—that may be transmitted based on the following equation:

[0039] where hj;s' are i.i.d. complex Gaussian random variables, the feedback metric is a N-tuple vector with the ith element corresponding to the channel quality for the ith transmitted antenna. Each element, denoted as C;, should be proportional to the product of the number of bits in a modulated symbol and the effective rate for the ith antenna.

[0040] For a given realization of channel matrix H, the transmission follows the following sequence. After obtaining channel matrix H from the channel estimator, the receiver computes the metric regarding the channel condition for each individual transmit antenna. These resulting metrics form an N-tuple vector, denoted as [C1; C2, . . . , CN

[0044] where NInfo b;ts is the total number of information bits transmitted, and Ncode block; is the number of information code blocks can be supported on the ith transmit antenna. The transmitter encodes the NInfo b;ts into N =n*NInfo b;ts coded bits using any type of channel coding schemes. Various channel coding schemes may be employed, including Turbo code, convolutional code, and Block codes, such as BCH and Reed Solomon code, for example. Thereafter, the coded bits are interleaved and distributed to the N transmit antennas. The number of coded bits to be distributed to the ith antenna is Ncode blocki *Nbpcb, for i=l, . . . , N. The effective rate for each antenna may be computed using the following equation: