HK1101740A - A method for transmitting multiple streams in wireless broadcast networks - Google Patents

Description

Method for transmitting multiple streams in a wireless broadcast network

Claiming priority in accordance with 35U.S.C § 119

This patent application claims priority to a provisional application filed on 28.1.2004 under application number 60/540,310 entitled "HIERARCHICAL CODING IN AMULTI-FREQUENCY BROADCAST NETWORK", which was assigned to the assignee of the present application and is hereby expressly incorporated by reference.

Technical Field

The present invention relates generally to broadcast systems, and more particularly to broadcasting content from transmitters from different geographical areas.

Technical Field

Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). For example, such a multiple access system includes: code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems.

Wireless communication systems also employ broadcast systems in which a portion of the forward link resources are dedicated to broadcasting content. In a broadcast system, all receivers process data received over a dedicated forward link (i.e., the frequency tones that make up the shared channel) as if the information were targeted for the receiver. Typical broadcast systems do not require any confirmation from the recipient regarding the receipt of the data. However, system operators typically configure an AP (i.e., an access point) to use low data rates (e.g., repeating transmission data packets that make up the content) and high power to ensure that all mobile stations within the coverage area of the base station receive the content, including all mobile stations that are far from the base station. However, in general, only mobile stations operating far from the current serving base station require a low data rate. Therefore, all mobile stations operating near the base station cannot enjoy higher data rates.

Therefore, there is a need for a method of managing broadcast resources so as to reduce coverage holes (coverage holes).

Disclosure of Invention

Accordingly, the present application provides a method and apparatus for: the received content is converted into a first stream and a second stream, the first stream is transmitted with a first tone, and the second stream is transmitted with an orthogonal scheme. A more complete appreciation of all the advantages and scope of the present invention can be obtained by a review of the accompanying drawings, the detailed description of the invention, and the appended claims.

Drawings

The features, nature, and advantages of the present invention will become more apparent by reference to the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

fig. 1 presents a schematic view of a wireless multiple-access communication system;

FIG. 2 is a block diagram of a communication system;

FIG. 3 illustrates an exemplary frame of a communication system; and

fig. 4 shows a flow of broadcasting content with two streams.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The word "listening" as used herein refers to a terminal receiving and processing data on a given channel.

Fig. 1 shows a schematic diagram of a wireless multiple-access communication system 100 employing multi-carrier modulation. The illustrated system 100 includes access points, e.g., 102a and 102b, that communicate with a plurality of access terminals 130a-130 b. For simplicity, only two access points 102a and 102b and two access terminals 130a-130b are shown in fig. 1. For ease of discussion, when referring to a single Access Terminal (AT), 130x is used; when referring to a single Access Point (AP), 102x will be used. The constituent components of access terminal 130x and access point 102x are described below with reference to fig. 2.

For ease of illustration, AP102a serves service area 1 and AP102b serves service area 2. The service area of AP102a is defined by 106, having a radius vector 120; the service area of AP102b is defined by 108, having a radius vector 122. The zones 106 and 108 are served with elementary streams of the broadcast system, as described below. Note that 106 and 108 assume that there is no interference. Once APs 102a and 102b are placed adjacent to each other, as shown in fig. 1, the service area is reduced, as defined by coverage black hole 116. In addition, APs 102a and 102b define service zones 110 and 112, respectively, and use a layered mechanism for zone services (e.g., using both enhancement and base streams), as discussed below.

As described above, the coverage hole 116 is shown to illustrate the area where signals from AP102a and AP102b interfere with each other. For ease of illustration, the coverage hole boundary 114 is shown to define the coverage hole 106. As shown in fig. 1, an AT130b operating within the coverage hole boundary 114 will not be able to receive content.

Access point 102x is an electronic device used for communicating with one or more user access terminals and may also be referred to as a base station, a base terminal, a fixed station, a base station controller, a transmitter, or some other terminology. In the following description, an access point, a base terminal, and a base station may be used interchangeably. The access point 102x may be a general purpose computer, a standard laptop computer, a fixed terminal, an electronic device that transmits, receives, and processes data according to the air interface methods defined by OFDMA, CDMA, GSM, WCDMA, etc., or an electronic module including a computer chip that is controlled by a controller or processor to transmit, receive, and process data according to the air interface methods defined by OFDMA, CDMA, GSM, WCDMA, etc.

The AT130x is an electronic device that communicates with an access point via a communication link. The AT130x may also be referred to as a terminal, user terminal, remote station, mobile station, wireless communication device, recipient terminal, or other terminology. The AT130x, mobile terminal, user terminal, terminal may be used interchangeably in the following description. Each AT130x may communicate with one or more access terminals via the downlink and/or uplink AT any given moment. The downlink (i.e., forward link) refers to transmission from the access point to the AT130x, and the uplink (i.e., reverse link) refers to transmission from the AT130x to the access point. The AT130x may be a standard laptop computer, a personal electronic organizer or assistant, a mobile telephone, a cellular telephone, an electronic device that transmits, receives and processes data according to air interface methods defined by OFDMA, CDMA, GSM, WCDMA, etc. systems, or an electronic module including one or more computer chips controlled by a controller or processor that transmits, receives and processes data according to air interface methods defined by OFDMA, CDMA, GSM, WCDMA, etc. systems.

The system controller 140 is coupled to access points and may also be coupled to other systems/networks (e.g., packet data networks). The system controller 140 coordinates and controls the access points to which it is connected. Via the access points, the system controller 140 also controls the routing of data between these terminals and users connected to other systems/networks. The system controller 140 can be used to update the transmit information for the base and enhancement streams.

Fig. 2 is a block diagram illustrating an embodiment of two access points 102x and 102y and an AT130x in a multiple access multi-carrier communication system 200. In access point 102x, a Transmit (TX) data processor 214 receives content data from a data source 212 as well as signaling and other information from a controller 220 and a scheduler 230. These different types of data may be transmitted over different transmission or broadcast channels. TX data processor 214 encodes and modulates the received data with multi-carrier modulation (e.g., OFDM) to provide modulated data (e.g., OFDM symbols). For example, the controller 220 converts the content into two data streams: a base stream and an enhancement stream. The controller 220 modulates the stream based on a predetermined scheme. A transmitter unit (TMTR)216 then processes the modulated data to generate a downlink modulated signal that is then transmitted from an antenna 218.

Terminal 130x receives the modulated signal via antenna 252 and provides it to a receiver unit (RCVR) 254. Receiver unit 254 processes and digitizes the received signal to provide samples. A Receive (RX) data processor 256 then demodulates and decodes the samples to provide decoded data, which may include recovered traffic data, messages, signaling, and so on. Traffic data may be provided to a data sink 258 and carrier assignment information transmitted for the terminal may be provided to a controller 260.

The controller 260 processes the received data stream based on information provided by the AP102x during registration. For each active terminal 130, a TX data processor 274 receives traffic data from a data source 272 and signaling and other information from controller 260. The various types of data are coded and modulated by TX data processor 274 using the assigned carriers and further processed by a transmitter unit 276 to generate an uplink modulated signal that is then transmitted from antenna 252.

At access point 102x, the transmitted and modulated signals from the terminals are received by antennas 218, processed by receiver units 232, and demodulated and decoded by an RX data processor 234. Receiver unit 232 may estimate the received signal quality (e.g., the received signal-to-noise ratio (SNR)) for each terminal and provide this information to controller 220. The controller 220 can then derive the PC commands for each terminal to maintain the received signal quality for that terminal within an acceptable range. RX data processor 234 provides the recovered feedback information (e.g., the required transmit power) for each terminal to controller 220 and scheduler 230.

For clarity, the techniques described herein are described in conjunction with an OFDMA system that uses Orthogonal Frequency Division Multiplexing (OFDM). In this system, for the forward link, signaling information, content data, etc. are sent in several frames. Fig. 3 shows a frame 302 used in an OFDMA system. The frame is defined by frequency and time. Within each frame, a plurality of tones, e.g., 304, 306, and 308, are defined for transmitting data based on available resources. The tone includes a frequency value for the duration. The frequency value is determined by the operator based on the available resources. As will be described in detail below, to transmit streams with layered modulation, tones 304 may be used, wherein two streams may be layered for transmission. An orthogonal scheme is used in which the first AP102x uses tone 306 and the second AP102x uses tone 308. Thus, depending on the associated service area of the AT130b, an AT130b operating within the coverage black hole may discard information received on tones 306 or 308. For example, if the AT130b is associated with server area 2 (served by the second AP102 x), the AT130b will ignore the tone 306 sent by the first AP102 x.

According to one embodiment, hierarchical modulation (also referred to as a hierarchical scheme) is employed in a broadcast system. Layered modulation involves transmitting multiple streams together, where each stream is directed to a group of users with a particular minimum channel quality. Users with better channel quality (users near AP102 x) will be able to decode more than one stream, thereby achieving higher data rates. The objective of layered modulation is to provide better throughput within the channel, since users that are well within the service area are likely to have better channels. Combining this with the trade-off provided by reuse, the basic idea behind our proposal can be summarized as: in systems that utilize layered modulation, different reuse techniques are used for different streams.

For simplicity, the description is made with an OFDM system. Note that the methods described herein may be used in any other system that provides broadcast capability and orthogonalization capability between transmitters. Further, for one service area, only one AP102x is used, and for ease of illustration, two service areas are used here, as shown in fig. 1 above. Further, broadcasting is done using OFDM, and reuse is achieved by allocating disjoint groups of tones to each AP102 x. The number of tones in each group is equal. Assuming that the signal from each AP102x passes through an Additive White Gaussian Noise (AWGN) channel, layered modulation involves transmitting two streams, the base stream directed to all users in the service area and the enhancement stream directed to users with better signal-to-noise ratio (SNR).

Assume that the OFDM scheme includes using 2N data tones. The 2N tones are divided into two disjoint sets, N_b，1And N_b，2Each of which has N tones. At the first AP102x, the symbols sent on the different tones are represented as:

img id="idf0001" file="A20058000989800121.GIF" wi="304" he="25" img-content="drawing" img-format="GIF"/

img id="idf0002" file="A20058000989800122.GIF" wi="257" he="26" img-content="drawing" img-format="GIF"/

wherein x is_b，1And x_b，2Are symbols from the base stream and the enhancement stream (i.e., a layered scheme) having power P, respectively_b，1And P_e，1. In other words, the base stream and enhancement stream are both at N_b，1Transmitted on one tone, while only the enhancement stream is on the remaining N_b，2Transmitted on one tone. Note that the power allocated to the base stream is typically greater than the power allocated to the enhancement stream, and the overall constraint must be met:

NP_b，1+2NP_e，1equation 1 ═ constant

Symbols from the second service area can be represented in a similar manner, where the elementary stream is at N_b，2One tone and the enhancement stream is transmitted on all tones.

Now consider the received symbol at tone k at any point in service area 1:

y(k)＝s₁(k)+βs₂(k)+n(k)

where β represents the ratio of the signal strength from the second AP102x to the signal strength from the first AP102x, and n (k) is the variance σ²Gaussian noise, parameters beta and sigma²Depending on the location in the coverage area. Thus, for N_b，1For the tone group in (2), the interference observed by the receiver comes from the enhancement streams of both service zones, but not from the base stream. Decoding of the base stream treats the two enhancement streams as additive interference. Once the base stream is decoded, it is subtracted from the received symbols so that the interference observed by enhancement stream 1 comes from enhancement stream 2 on all tones. In addition, for N_b，2The same is true for tones in (2) and interference from base stream 2. Decoding of the enhancement stream treats these as additive interference. Interference from base stream 2 may severely degrade the performance of enhancement stream 1, but the key to the problem is that enhancement stream 1 is expected to be decoded only at an inner point, and therefore, will significantly attenuate base stream 2.

We can express the performance of the above scheme in terms of theoretical spectral efficiency based on shannon capacity and AWGN channel. The rate of the base stream depends on the worst case SINR (signal to interference plus noise ratio) in service area 1, where SINR includes interference from the two enhancement streams. Assuming p represents a point at the edge of coverage, the noise variance is σ_p ²The interference is attenuated by p. The spectral efficiency of the base stream is expressed as:

img id="idf0003" file="A20058000989800131.GIF" wi="305" he="62" img-content="drawing" img-format="GIF"/equation 2

Therein, a factor 1/2 appears because we have used only half the tones.

Also, the rate of the enhancement stream is subject to the worst case SINR in the smaller coverage area, where SINR includes base stream 2 and enhancement stream 2. Suppose for the enhancement flow, σ_q ²And beta_qIs the variance of the noise at a point covering the edge. Note that since this footprint is smaller than that of the elementary stream, we get β_q＜β_pAnd σ_p ²＜σ_p ². Thus, the total interference at point q is small and the elementary stream is decodable at q. At point q, the rate of enhancement flow is expressed as:

img id="idf0004" file="A20058000989800132.GIF" wi="489" he="64" img-content="drawing" img-format="GIF"/equation 3

For a typical interference scenario, it can be seen that the above-mentioned rates for the base stream and enhancement stream are greater than the rate for the case where the base stream is not reused (i.e., all 2N tones are used for the base stream and enhancement stream) and the rate for the reuse factor of 2 (i.e., only N tones are used for the base stream and enhancement stream at each transmitter).

Typically, the service provider specifies the physical location of the AP. Thereafter, it is identified that multiple APs are likely to have coverage holes, as described above. For these APs, the tones used to perform the disclosed embodiments may be preselected, modified wirelessly, or dynamically controlled by the access controller.

The flow 400 given in fig. 4 does not show broadcasting content with two streams. AP102x performs the steps of flow 400 using at least one of the various components described in fig. 2, e.g., controller 220, scheduler 230, memory 222, TX data processor 214, RX data processor 234, etc. In one embodiment, the pre-selected AP102x uses the techniques described above. At step 402, the AP102x converts the content into two streams, a first stream (i.e., the enhancement stream) and a second stream (i.e., the base stream). These streams may be series of data packets of content. The enhancement stream is modulated to provide an additional data rate within a smaller footprint than the base stream. At step 404, the AP102x transmits the two streams using a layered scheme, as described above. At step 406, AP102x transmits the base stream using the pre-selected tones. The frequency of the pre-selected tone is orthogonal to the frequency of the tones used by one or more neighboring APs 102 x. In another embodiment, the same frequency may be used to transmit the elementary stream, with the time (symbol) of transmission being orthogonal to the adjacent AP102 x.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination of hardware and software. For a hardware implementation, the processing units (e.g., controllers 220 and 270, TX processor 214 and RX processor 234, etc.) used for these techniques may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. These software codes may be stored in a memory unit (e.g., memory 222 in fig. 2) and executed by a processor (e.g., controller 220). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

Headings are included herein for reference and to facilitate locating particular sections. These headings are not intended to limit the scope of the concepts described therein under, which concepts may be applied to other portions of the entire specification.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (31)

1. A method for broadcasting content in a wireless communication system, the method comprising the acts of:

converting the content into a first stream and a second stream;

transmitting the first stream with a first tone; and

transmitting the second stream with an orthogonal scheme.

2. The method of claim 1, wherein the act of transmitting the second stream with an orthogonal scheme further comprises the acts of:

utilizing a second tone that is orthogonal to tones used by adjacent access points.

3. The method of claim 1, further comprising the acts of:

the second stream is transmitted with the first stream using the first tone.

4. The method of claim 1, wherein,

the act of sending the first stream comprises an act of sending the first stream at a first data rate; and

the act of sending the second stream comprises an act of sending the first stream at a second data rate.

5. The method of claim 3, wherein,

the act of sending the first stream comprises an act of sending the first stream at a first data rate; and

the act of sending the second stream comprises an act of sending the first stream at a second data rate that is lower than the first data rate.

6. The method of claim 1, wherein the act of sending the second stream further comprises the acts of:

for the second stream, a power level different from the power level used for the first stream is used.

7. The method of claim 3, further comprising the acts of:

layering the first stream and the second stream on the first tone.

8. The method of claim 1, wherein the act of transmitting further comprises an act of transmitting according to a Code Division Multiple Access (CDMA) scheme.

9. The method of claim 1, wherein the act of transmitting further comprises an act of transmitting according to an Orthogonal Frequency Division Multiplexing (OFDM) scheme.

10. The method of claim 1, wherein the act of transmitting further comprises an act of transmitting according to an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

11. An apparatus for broadcasting content in a wireless communication system, the apparatus comprising:

a module to convert the content into a first stream and a second stream;

means for transmitting the first stream with a first tone; and

a module that transmits the second stream with an orthogonal scheme.

12. The apparatus of claim 11, wherein the means for transmitting the second stream comprises:

a module that utilizes a second tone that is orthogonal to a tone used by an adjacent access point.

13. The apparatus of claim 11, further comprising:

means for transmitting the second stream with the first stream using the first tone.

14. The apparatus of claim 11, wherein,

the means for transmitting the first stream comprises means for transmitting the first stream at a first data rate; and

the means for transmitting the second stream comprises means for transmitting the first stream at a second data rate.

15. The apparatus of claim 13, wherein,

the means for transmitting the first stream comprises means for transmitting the first stream at a first data rate; and

the means for transmitting the second stream comprises means for transmitting the first stream at a second data rate that is lower than the first data rate.

16. The apparatus of claim 11, further comprising:

means for transmitting the second stream using a power level different from a power level used for the first stream.

17. The apparatus of claim 13, further comprising:

means for layering the first stream and the second stream on the first tone.

18. The apparatus of claim 11, wherein the means for transmitting further comprises means for transmitting according to a Code Division Multiple Access (CDMA) scheme.

19. The apparatus of claim 11, wherein the means for transmitting further comprises means for transmitting according to an Orthogonal Frequency Division Multiplexing (OFDM) scheme.

20. The apparatus of claim 11, wherein the means for transmitting further comprises means for transmitting according to an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

21. An apparatus in a wireless communication system, comprising:

an electronic device that converts received content into a first stream and a second stream, transmits the first stream with a first tone, and transmits the second stream with an orthogonal scheme.

22. The apparatus of claim 21, wherein the electronic device utilizes a second tone that is orthogonal to a tone used by an adjacent access point.

23. The apparatus of claim 21, the electronic device further to send the second stream with the first stream using the first tone.

24. The apparatus of claim 21, wherein,

the electronic device also transmits the first stream at a first data rate; and

the electronic device also transmits the first stream at a second data rate.

25. The apparatus of claim 23, wherein,

the electronic device also transmits the first stream at a first data rate; and

the electronic device also transmits the first stream at a second data rate that is lower than the first data rate.

26. The apparatus of claim 21, wherein the electronic device further uses a power level different from the power level used for the first stream.

27. The apparatus of claim 23, the electronic device further to tier the first stream and the second stream over the first tone.

28. A machine-readable medium comprising instructions, which when executed by a machine, cause the machine to perform operations comprising:

converting the content into a first stream and a second stream;

transmitting the first stream with a first tone; and

transmitting the second stream with an orthogonal scheme.

29. The machine readable medium of claim 28, wherein the machine readable instructions that cause transmitting the second stream with an orthogonal scheme further comprise instructions to:

utilizing a second tone that is orthogonal to tones used by adjacent access points.

30. A broadcast system, the system comprising:

a first access point and an adjacent access point;

the first access point converts content into a first stream and a second stream, transmits the first stream with a first tone, and transmits the second stream with a second tone.

31. The broadcast system of claim 30, wherein the second tone used by a first access point is orthogonal to the tone used by the neighboring access point.