WO2010012108A1

WO2010012108A1 - System and method for cooperative coded data multicast

Info

Publication number: WO2010012108A1
Application number: PCT/CA2009/001091
Authority: WO
Inventors: Pin-Han Ho; Pei Man James She
Original assignee: Pin-Han Ho; Pei Man James She
Priority date: 2008-07-31
Filing date: 2009-07-31
Publication date: 2010-02-04

Abstract

A system and method for cooperative coded multicast (CCM) is provided. The system enables the transmission of a data bitstream over a wireless network to one or more receivers. The system includes a scalable bitstream coding means for separating the data bitstream into a layered bitstream, a protection coding means for applying protection coding to the layered bitstream to create a protected bitstream, a superposition coding means for applying one or more different modulation schemes to the protected bitstream to create a modulated bitstream, and a coding means for cooperative transmission operable to apply one or more orthogonal codes at a plurality of transmitters for cooperatively transmitting the modulated bitstream to the one or more receivers.

Description

SYSTEM AND METHOD FOR COOPERATIVE CODED DATA MULTICAST

PRIORITY

This application claims priority to United States Patent Application 61/129,937 filing July 31 , 2008.

FIELD OF THE INVENTION

The present invention relates to wireless data multicasting. The present invention more specifically relates to providing a cooperative coded multicast signal for wireless transmission.

BACKGROUND OF THE INVENTION

Advanced broadband Internet access and scalable video technologies have made Internet Protocol Television (IPTV) possible as a commercial service. For efficient and scalable video delivery of IPTV services, commercial deployment is conventionally based on managed content delivery (overlay) or distributed networks consisting of media servers and caches/gateways with a higher operational cost. Innovative and more cost-effective techniques using peer-to-peer (P2P) or P2P overlay approaches, such as MediaGrid [1] and PPLive [2], have also evolved to deliver streaming videos economically in public IP networks but these techniques currently lack reliability assurance.

Regardless of which of these approaches is to become the architecture for video delivery in future wired IPTV infrastructures, next-generation IPTV services are likely to be offered in a hybrid of wired/wireless environment due to the vibrant broadband access technologies based for example on IEEE 802.16 (or WiMAX) [3] and Ethernet Passive Optical Networks (EPON) [4]. Extending IPTV services over such access networks not only provides operators with the highest economies of scale for their operations to secure bigger successes in video businesses, but also creates additional revenue sources in mobile solutions and/or by servicing areas with uneconomical last-mile wired access infrastructure.

An EPON consists of a central Optical Line Terminal (OLT) and multiple Optical Network Units (ONUs) that are connected to the OLT through fibers of a tree topology. Given a certain optical split ratio, only a limited number of ONUs can be connected to an optical splitter and then to a common OLT. For example, a 1 : 16 splitter can maximally connect 16 ONUs. As a root node, the OLT is often located in a Central Office (CO) which provides an access to the core IPTV network that is beyond an EPON-WiMAX access network.

Within the EPON-WiMAX access network, an EPON ONU and a WiMAX transmitters or base station (BS) are integrated into a single device box, called ONU-BS [4]. In addition to hardware cost saving, such integration achieves a flat control plane and seamless integration between the EPON and WiMAX systems, where signaling and control messages are exchanged directly between the OLT and the end users or receivers, which could be fixed stations or mobile stations (MSs). Beside directly extending the comprehensive class of services for various traffic type (i.e. UGS, rtPS, nrPS and BE) defined in WiMAX standards, Multicast/Broadcast Services (MBS) [5] should also be adopted from the standards to support both unicast and multicast applications in the EPON-WiMAX networks. Due to the tree topology of EPON and the broadcast nature of WiMAX, the EPON-WiMAX access networks are ideal to provision bandwidth-intensive IPTV content to multiple receivers simultaneously using wireless multicasting without duplicated deliveries, especially for on-going scheduled TV channels. However, there are new challenges to be addressed for preserving the use of multicasting in such integrated networks for IPTV services.

An open problem in wireless multicasting is to cope with multi-user channel diversity. Recent research efforts have attempted to address this issue utilizing advanced coding techniques. A 2- level superposition coded multicast (SPCM) scheme for delivering IPTV content over WiMAX was introduced [6], in which video bitstreams of base and enhancement quality layers in each video frame are embedded together within a single SPCM signal, such that receivers can demodulate and decode at least the basic video quality at any moment even when their channels are not-so-good, whereas receivers with good channel conditions can decode both quality layers of video bitstreams from the same SPCM signal.

In this scheme, instead of using one modulation scheme for a multicast transmission at a time, each multicast signal is generated at the channel by superimposing a base quality layer of video bitstreams modulated by BPSK as well as an enhancement quality layer of video bitstreams modulated by a higher-order modulation such as 16QAM. Thus, a receiver can either obtain the basic video quality of an IPTV channel by partially decoding the multicast signal for those bitstreams modulated in BPSK when the channel is not good enough; or obtain the full video quality from all bitstreams modulated in BPSK and 16QAM by successfully decoding the whole SPCM signal when the channel is good. The 2-level superposition is not restricted to the modulations of BPSK and 16QAM only. It is also applicable to other modulations such as QPSK and 64QAM supported in WiMAX standards. It is preferably designed to use a lower order modulation in the 1^st level of the superimposed signal due to a lower signal-to-interference-plus- noise (SINR) requirement for decoding some information from the signal by a receiver with the bad channel condition. The scheme preserves the use of video multicasting for IPTV services over WiMAX under the multi-user channel diversity for a more scalable system capacity, while it also maintains the base video quality for receivers during the moments that their channel conditions are not good. In addition, the adoption of SPCM by a WiMAX BS can take advantage of the bitstream data dependency of base and enhancement layers in the task of video multicasting.

Similarly, a cross-layer approach using multi-resolution modulation [7] incorporates adaptive power allocation and channel coding strategies by considering the interference-limited and bandwidth-limited characteristics of a CDMA system. In this method, the video encoder is effectively matched with an embedded multi-resolution modulation scheme to simultaneously deliver a basic quality-of-service (QoS) to less capable receivers while maximizing both the QoS for more capable receivers and the system capacity.

Unfortunately, solutions based on superposition coding or multi-resolution modulation alone are only effective to address the channel diversity of a group of multicast receivers, and an alternate approach is required in order to recover any data lost during poor channel conditions due to channel fluctuation.

What has not been explored is the possibility of integrating physical-layer and application-layer coding techniques, as well as some unique features of modern access networks, such as the employment of cooperative communications among distributed ONU-BSs in the EPON-WiMAX networks. What is needed is a cooperative cross-layer approach to effectively improve efficiency and reliability of multicast video quality over wireless networks.

SUMMARY OF THE INVENTION The present invention provides a system for transmitting a data bitstream over a wireless network to one or more receivers, the system characterized by: (a) a scalable bitstream coding means for separating the data bitstream into a layered bitstream, each layer representing a different quality representation of the data bitstream; (b) a protection coding means for applying protection coding to the layered bitstream to create a protected bitstream; (c) a superposition coding means for applying one or more different modulation schemes to the protected bitstream to create a modulated bitstream; and (d) a coding means for cooperative transmission operable to apply one or more orthogonal codes at a plurality of transmitters for cooperatively transmitting the modulated bitstream to the one or more receivers.

The present invention also provides a method for transmitting a data bitstream over a wireless network to one or more receivers, the method characterized by: (a) separating the data bitstream into a layered bitstream, each layer representing a different quality representation of the data bitstream; (b) applying protection coding to the layered bitstream to create a protected bitstream; (c) applying one or more different modulation schemes to the protected bitstream to create a modulated bitstream; and (d) applying one or more orthogonal codes to a plurality of transmitters for cooperatively transmitting the modulated bitstream to the one or more receivers.

In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system in accordance with the present invention.

FIG. 2 illustrates a receiver receiving a cooperative transmission from a plurality of transmitters.

FIG. 3 illustrates layered MDC applied on a group of frames encoded by scalable data coding.

FIG. 4 illustrates coded video multicast in one example implementation of the present invention. FIG. 5 illustrates encoding of video bitstreams of a quality layer by modified layered MDC at the source.

FIG. 6 illustrates a multicast over an EPON-WiMAX access network with three ONU-BSs.

FIG. 7 illustrates the SINR for each quality layer at the receivers in the three interested areas under the best achievable modulation schemes for the two quality layers in a particular example implementation of the present invention.

FIG. 8 illustrates an example of a multi-hop cooperative video transmission for multicast/broadcast to a single receiver in accordance with the present invention.

DETAILED DESCRIPTION

Overview

The present invention provides a system and method for cooperative coded multicast to overcome existing problems affecting wireless multicast, including multi-user channel diversity, short-term channel fluctuations and inter-cell interferences.

The cooperative coded multicast of the present invention (CCM) achieves efficient and reliable data transmission over wireless networks. CCM provides a wireless multicast architecture that is operable on existing wireless networks by integrating the methods described herein, and implementing CCM using existing technologies or future wireless technologies. For example, in one particular implementation of the present invention, it is operable to achieve efficient and reliable IPTV services over existing EPON-WiMAX integrated networks but can also be adapted for future wireless networks include future integrated wireless networks. Further implementations enable wireless digital signage, wireless gaming, wireless advertisement broadcasting/multicasting services, or any multimedia content (video/audio/text/data or any of their combination) with multiple quality levels/layers to be broadcasted/multicasted by a plurality of transmitters.

The system of the present invention integrates coding for cooperative transmission at the transmitted level, superposition coding in the media access control (MAC) and physical (PHY) layers and scalable bitstream coding at the application-layer with superposition coded multicast , in order to provide robust and efficient data multicast transmissions.

Communications between known wireless network components may be configured to enable the CCM processes described herein. The system of the present invention may be understood as a network manager or other similar network utility that is operable to apply the CCM processes to a wireless network. The present invention can also be understood as a wireless multicast service using the techniques described in the present invention.

CCM for data multicasting over a wireless network includes coding for cooperative transmission at the base stations, superposition coding at the channel and a scalable bitstream coding at the application-layer. The coding for cooperative transmission may for example be space-time coding (STC) and the scalable bitstream coding may be modified layered MDC. The wireless network may for example be EPON-WiMAX and the base stations may for example be ONU- BSs.

Coding for cooperative transmission is used to leverage the intercell interferences effect to increase the probability of signal reception at a receiver. The present invention uses the interferences carrying the same data from a plurality of transmitters or base stations (BSs) to enhance the signal of the data received by a receiver or subscriber station (SS). In particular, the present invention leverages the inter-cell interference effect for enhancing a signal transmitted to a receiver. In the present invention, the coding for cooperative transmission, which could for example be space-time coding based cooperative transmission, enables a receiver to combine and utilize signals containing the same data received from a plurality of transmitters, even though they may not received at the same time. In the case of STC at the transmitters, it enables a plurality of transmitters to transmit the same data using orthogonal codes. The use of orthogonal codes reduces the destructive interference effect from the transmitters. A receiver is correspondingly more likely to receive the data by the additive power from the transmitters. It should be noted that the present invention is not limited to the use of space-time coding, as long as the coding for cooperative transmission enables a receiver to combine and utilize signals containing the same data received from a plurality of transmitters, even though they may not received at the same time. Thus, a receiver can for example obtain lost data, for example a lost MDC packet if MDC is used, through the constructive interferences from other transmitters containing the same layer of data. A receiver can obtain the required minimum amount or number of MDC packets (e.g. K_/ of N) of the protected data, for example scalable video data, in a layer to reconstruct the original video of layer /. Hence, a transmitter can actually send less data with less than N transmissions/MDC packets if the target receiver can be provisioned to receive the minimum amount or number of MDC packets for the required layers of video data. Consequently, transmission resources in each transmitter can then be free for other services. This also enables a receiver moving from the wireless coverage of an existing associated transmitter to the wireless coverage of a newly associated transmitter to seamlessly reconstruct the video data of layer / as long as the minimum amount of video data of layer / can be obtained during the handover/movement across transmitters. It should be understood that these advantages are provided by the use of STC in the present invention. It is not required to provide MDC or protection coding on the data to provide these advantages.

In one particular implementation of the present invention, STC cooperative transmission among multiple ONU-BSs may be embedded in the system of the present invention to explore the unique feature of EPON-WiMAX integration and take advantage of the centralized coordination by the OLT, where a robust, efficient, and high-quality data multicasting under the EPON- WiMAX integration may be achieved. Thus the present invention may be implemented for both data broadcasting and multicasting scenarios in modern broadband wireless access networks, as both suffer from the problems of long-term channel diversity, short-term fluctuations, and inter- cell interference.

It should be understood that while the present invention is particularly advantageous for transmission of scalable video bitstreams to enable IPTV transmission over a wireless infrastructure, the system and method of the present invention is easily adapted to transmission of any other type of layered data transmission application to overcome the issues of long-term channel diversity, short-term fluctuations and inter-cell interference including those applications described above.

CCM System FIG. 1 illustrates a system in accordance with the present invention. The CCM system comprises a network manager 1 operable to receive a data bitstream from a data source 9. The network manager 1 is linked to a plurality of transmitters 1 1 , 13, 15 that are operable to transmit a wireless signal to one or more receivers 17, 19, 21 , 23.

The network manager 1 includes a scalable bitstream coding utility 3 and coding for cooperative transmission utility 7. The scalable bitstream coding utility 3 provides a scalable data bitstream from the data bitstream received from the data source 9. A protected bitstream for each layer is generated based on the scalable data bitstream by the protection coding utility 5. The coding for cooperative transmission utility 7 is operable to provide the transmitters 11, 13, 15 with orthogonal codes for enabling cooperative transmission.

The transmitters are operable to receive from the network manager 1 the scalable data bitstream and orthogonal codes for cooperative transmission. The transmitters include multi-resolution modulation utility 33 for generating a multi-resolution wireless broadcast/multicast signal embedding the scalable data bitstream of a plurality of quality layers. The transmitters also include a cooperative transmission utility 31 for generating a wireless multi-resolution signal for transmission of the scalable data bistream based on the orthogonal code provided to the transmitter 1 1 , 13, 15 from the network manager 1.

The transmitted signal is received at one or more receivers 17, 19, 21, 23 which each include a cooperative transmission decoder 35, multi-resolution demodulator 37, protection decoder 39 and scalable bistream decoder 41 for producing a representation of the original data bitstream.

Furthermore, depending on the implementation and the network, some receivers may be operable to forward or retransmit a received signal. This enables the receivers to assist in providing to other receivers a cooperatively coded multicast signal.

In particular, the present invention enables a receiver in an area where more than one transmitted signal is received to leverage inter-cell interferences to receive a stronger signal than in the prior art. As shown, receiver 17 within a coverage area 25, 27, 29 covered by the transmitters 11, 13, 15 may use the received cooperative transmissions containing the same bitstream data for producing a better representation of the original data bitstream. This is achieved because each output signal to the receiver is better decoded from multiple cooperative signals containing the same data, in which more protected bitstream of each layer can be decoded for better recovery of lost bitstream portions.

It should be understood that as depicted SSl 17, SS3 21 and SS4 23 also include the components described for SS2 19. Similarly BS2 13 and BS3 15 include the components described for BSl 11.

It should be understood that while FIG. 1 illustrates an integrated network manager and transmitters, it is contemplated that the functions performed by the network manager and transmitters could be implemented on a distributed basis, for example the scalable bitstream coding, superposition coding and coding for cooperative transmission could be implemented on one or more systems that are linked together to enable CCM. The network manager can be implemented as a separate device/system that is linked or accessed by the transmitters or the system generating the data source from time to time or on a continuous basis. Additionally, an intermediary device or the transmitters may provide some or all of the functionality of CCM including, for example, the scalable bitstream coding or the coding for cooperative transmission if parameters are synchronized through a central control unit, for example the network manager.

Scalable Bitstream Coding and Superposition Coding

The use of scalable bitstream coding contributes not only to the robustness of the data quality, but also to mitigate the channel condition fluctuation due to user mobility. The scalable bitstream coding may be any (n, k_/) protection or erasure coding to recover the data on layer / as long as at least k_/ packets out of n packets are successfully received, where k_/ is the k value specifying the minimum number of packets to recover all the data of layer /. In one particular implementation of the present invention, the scalable bitstream coding can be implemented by MDC based on Reed-Solomon coding.

To improve robustness on video quality and overcome the channel fluctuations due to short-term fading, scalable bitstream coding, for example MDC, for providing erasure coding may be provided at the application layer. The idea of many previous MDC schemes was to encode the data into vV set of packets (or descriptions) for reconstructing the original data, which is then transmitted from a source to receiver(s) over channel(s) with spatial or temporal diversity to combat packet loss in wired infrastructure for a variety of application scenarios. A typical receiver can reconstruct the original data with minimal or certain distortion, not depending on particular MDC packets, but only the number of MDC packets successfully received from different routes or less correlated timeslots within the decoding duration.

In general, the more MDC packets a receiver obtains the better data reconstruction it enjoys. While MDC schemes for wired networks assume either complete loss or complete reception of the whole MDC packet, it has been found that in wireless communications it is more optimal to account for partially received MDC packets. Since MDC packets with protected units (PUs) containing bitstreams of multiple quality layers can be either completely lost or received as a whole in wired networks, the data of higher quality layers becomes totally useless if a lower quality layer fails to recover from its minimal required number of MDC packets as defined by a smaller K value. Conventionally, layered MDC therefore typically uses a small partition length Ki for a lower video quality layer while a larger length is selected for partitioning a higher layer (i.e. more protection overheads to the source blocks of a lower layer) because the final video reconstruction is more dependent on the lower layer of bitstream than the higher one. In other words, if a receiver successfully received K MDC packets, then all layers n such that K_n < K are recovered while all layers n with K_n > K are lost.

The layered MDC scheme of the present invention can include a priority encoding transmission (PET) technique as a packetization scheme that combines layered data coding, for example layered video coding, with unequal erasure protection. Layered MDC may be applied on the layered structure in a Group of Frames (GoF) encoded by scalable video codings, as shown in FIG. 3. Each GoF may be independently encoded into scalable bitstreams with multiple quality layers of different importance. The bitstream between the boundaries, bι._\ and bι, of each layer / may then be partitioned into source blocks of equal length K_/ bytes. Each source block of K_t bytes may be encoded and expanded into a series of protected units (PUs) of length N bytes using an (N Ki) Reed-Solomon (RS) code.

For example, there may be exactly L layers, i.e., / = 1, 2 L, which are indexed in an order of non-increasing importance such that layer / is protected with an (N, K_/) code. In general, the value of K_/ for partitioning layer / video bitstream is determined by various factors, including the significance of that layer for the final video reconstruction, the protection required by that layer in the transmission channel, etc. A smaller Ki means a better protection but more overhead for the bitstream data in that layer against loss/error. The PUs of each layer are then packetized by putting the n-th byte in each row of PUs belonging to that layer into the n-th MDC packet, where n = 1 , ... , N. In this sense, all these N MDC packets are equally important and it is the number of MDC packets received by the receiver that determines the reconstructed data quality of the GoF. The λ?-th MDC packet constitutes the n-th description of the GoF, which contains a certain amount of bitstream data of multiple quality layers in the GoF.

In the present invention, the layered MDC is modified, again counter-intuitive to what has been taught by the prior art, by providing a decreasing order of A^' values for each layer starting from a lower layer (i.e. N - K₁ < N - K₂ < ...< N - K, < ...< N - K_L), which is different from the conventional layered MDC scheme.

Superposition encoding of the CCM may be provided as follows, however other methods of superposition coding could also be used. The relatively lower layer bitstream may be protected by a lower-order modulation scheme with more robustness, for example BPSK, whereas the relatively higher layer bitstream may be protected by a higher-order modulation scheme providing higher bandwidth, for example 16QAM, which do not necessarily need a larger K for more redundancy. By using a decreasing K value for each next higher layer, it is highly possible to recover most or even all layers n such that K_n > K, even if the receiver only successfully received K MDC packets,

Coding for Cooperative Transmission

Multi-cell coding for cooperative transmission can effectively improve the perceived SINR of each user and eliminate the boundary effect especially when inter-cell interferences are serious. The conventional service provisioning scenario can be realized for the configuration shown in FIG. 2 where user A can only be associated with its home transmitter, for example its home ONU-BS, shown as ONU-BS-L The inter-cell interference due to power leakage from one cell to another is unfavorable to SINR of the users within the cell, particularly for the users in the overlapped boundary areas of the cells, such as spot A. In the case where ONU-BS-I is the home ONU-BS, SINR, « \ 0\og{Pj{P₂ + P, + N₀)), where P₁ is the power of ONU-BS-/ perceived at by user, and NQ is the averaged channel noise. However, in the present invention such inter-cell interferences can be avoided by exercising coding for cooperative transmission among neighboring transmitters. For example, in FIG. 2 by using the space-time coding technique, ONU-BS-I, -2, and -3 are assigned with orthogonal codes, and the user at spot A, which is the overlapped area of boundaries of the three cells and could be subject to a serious inter-cell interference in the conventional scenario, may now receive additive power rather than destructive interference from the three ONU-BSs. In this case, user A has its SINR SINR _A « 101og((/^> + P₂ + P,)/ N₀) .

Furthermore, although the coding for cooperative transmission may consume additional resources from all three transmitters, the total consumed capacity can be significantly reduced over the conventional technique. This is because the three transmitters can potentially take a more aggressive modulation scheme and subsequently consume less system capacity even if the three transmitters cooperatively provision a single service.

Cooperative Coded Multicast

CCM mitigates severe destructive impacts due to inter-cell interferences, multi-user channel diversity in multicasting, and short-term channel fluctuation resulting from a transmission from just a single transmitter. The present invention enables efficient, robust, and scalable data multicasting for wireless networks, including for example EPON-WiMAX integrated networks.

The scalable bitstream coding may be applied on scalable data bitstreams at the application layer, and superposition coding in the MAC and physical layers may work together with the coding for cooperative transmission. For example, CCM may use space time coding over multiple ONU- BS initiated at the OLT. The timing of multicasting the same data across distributed ONU-BSs may be aligned and controlled by the common associated OLT. As a result, the WiMAX multicast signals launched in the air will be multi-resolution modulated with MDC protections and cooperatively delivered through multiple ONU-BSs. CCM therefore promotes the maximum possible performance gain and economic scale for data multicast services, for example IPTV, under integrated EPON-WiMAX networks.

Coded Video Multicasting under a Single ONU-BS One major limitation of SPCM or any multi-resolution modulation alone is that a receiver can never receive/recover data of higher quality layers during the moment where it is under a "bad" channel condition. However, the present invention resolves this problem by optionally providing superposition coding at the channel and the scalability of video coding at the source, and arranging PUs generated by the modified layered MDC to be superimposed to form cross-layer coded multicast transmission blocks.

Coded video multicast in accordance with the present invention under a single ONU-BS may be provided as follows. Assuming for example that 2 quality layers are provided (though there could be any number) in the video bitstream of a GoF, PUs of bitstreams in layer 1 and 2 may be generated by the modified layered MDC using Reed-Solomon (RS) code with parameters K), A^ and N as shown in FIG. 4(a). PUs of layer 1 and layer 2 may then be queued in buffers Bl and B2, respectively, in the BS shown in FIG. 4(b) with the sequences according to their description orders. Starting with the first available timeslot for multicast transmission at time t = 1 , PUs of layer 1 belonging to the 1^st description in buffer Bl may be modulated with a lower order of modulation (for example BPSK), which can be demodulated with a lower SINR at a given bit error rate (BER). Concurrently, PUs of layer 2 in buffer B2 belonging to the 1^st description may be modulated by a higher order of modulation (for example 16QAM), which requires a higher SINR to demodulate for the same BER. Both modulated signals from buffers Bl and B2 may then be superimposed altogether to form a cross-layer coded multicast transmission block for the 1^st MDC packet to be launched in the wireless channel. Within each timeslot, the transmission rate of a selected modulation in the buffer for layer / should be fast enough to multicast all PUs belonging to a description of that layer. Otherwise, the size of a PU and the timeslot duration may be adjusted for long-term system stability. Similar procedures in generating such cross-layer coded multicast signals may be provided for each subsequent MDC packets in every GoF until the video multicast finishes.

Example Implementation of CCM

Optimally, CCM provides STC for cross-layer coded video multicasting described above. With orthogonal codes equipped in each distributed ONU-BS, enabling STC based cooperative transmission initiated by the OLT, a receiver could be provisioned by multiple ONU-BSs cooperatively and obtain aggregated power assigned for each layer of MDC protected bitstreams. As shown in FIG. 5, the video bitstream of a quality layer will be firstly encoded by the modified layered MDC at the source. The ONU-BSs, upon receiving the MDC bitstreams, will perform superposition coding on the bitstreams of different quality layers. The superimposed signal, which may for example correspond to a GoF of an IPTV channel, is further encoded using the assigned space-time code which is orthogonal to that used by the other ONU-BSs. Therefore, according to STC, a receiver receiving a signal from a plurality of ONU-BSs may perceive the aggregated power of each ONU-BSs, which yields a much higher SINR than in a conventional situation using a single ONU-BS. Due to the higher perceived SINR, the three ONU-BSs can adopt a pair of more aggressive modulation schemes in the two quality layers of video bitstreams under the cooperative provisioning scenario while ensuring that a receiver in the receiving a signal from a plurality of ONU-BSs can still decode the received signal.

In one particular implementation of the present invention, an IPTV channel is being multicasted over an EPON-WiMAX access network with three ONU-BSs as shown in FIG. 6. Two quality layers of video bitstream are provided for every GoF. Each ONU-BS is provided at the origin of a cell, and a receiver is operable to associate with and be served by at least one ONU-BS, for example its home ONU-BS, which is the ONU-BS closest to the receiver and therefore with the strongest SINR. An exponential path loss model with Rayleigh fading is assumed in determining the individual SINR of a signal from an ONU-BS to a receiver with the distance and allocated power. Polar coordinates P{r ,θ) are used with the home ONU-BS at the origin. The distance of a receiver at (r,θ) from the z-th ONU-BS at (r,6> ) can be expressed as

(I₁ (r, θ) = φ^+ r - 2)Ύ COS(O¹ - (9 ) .

Simulations are provided using MATLAB to obtain the highest achievable SINRs of each quality layer in the multicast signals for the scenarios with and without cooperative coded multicasting. Values may be chosen for the following parameters for simulating a wireless network implementation: channel condition of each receiver, channel fading parameters of each channel between a receiver and transmitter/receiver, transmission schedule and resource allocation of each transmitter/receiver, distance/location of each receiver with respect to each transmitter or another receiver, protection parameters utilized in each transmitter, synchronized orthogonal code used at each base station for each broadcast/multicast transmission, power allocation in each layer for multi-resolution modulation in each transmitter, scalable video coding and protection codes, timing, power and duration of interferences from base stations or receivers, and other standard and associated operational parameters of wireless network transmission with multi-transmitter and receivers, such as numbers of terminals, density, timing, etc. For example, the parameters chosen and fading channel environments from [12] may be used. The best pairs of modulation schemes with the optimized power of each quality layer in superposition coding are selected universally across all ONU-BSs in the EPON-WiMAX network. The video quality of a GoF perceived by a receiver depends on the total amount of receivable/recoverable bitstream of the GoF, which is further affected by the factors of bit error rates (or layer error rates) and the throughout of each received cross-layer coded multicast signal in both quality layers. These factors are essentially determined by the aggregated SINR of each quality layer perceivable by a receiver. Therefore, averaged SINRs of SSi, SS₂, SS₃, and SS₄ are measured in three interested areas Al , A2 and A3, for each quality layer with and without employing the cooperative communications over 5,000 timeslots simulated.

FIG. 7 illustrates the SINR for each quality layer at the receivers in the three interested areas under the best achievable modulation schemes for the two quality layers in this example implementation. For SSi and SS₂, CCM increases perceived required SINRs to support modulation in both quality layers of the multicast signals in the presence of the inter-cell interferences (i.e. 1 1.8dB and 1 1.4dB in average for base quality, and 7.OdB and 9.8dB in average for enhancement quality at SSi and SS₂ respectively). However, without CCM the implementation fails to provide the minimal SINRs for even the lowest order of modulation in any quality layer for SSi and SS₂ in both areas Al and A2 under interferences. On the other hand, the provisioning of CCM does not affect the SINR of the multicast signals perceived by SS₃ and SS₄ if there are no inter-cell interferences from the other ONU-BSs in area A3. However, SS₄ in area A3 only has the required SINR to support the lowest order of modulation, BPSK, for the base quality layer, but not enough SINR to support any modulation type for the enhancement quality layer. On the contrarily and interestingly, as shown in FIG. 7, although those SSs located at areas Al and A2 are subject to severe interferences from neighboring ONU- BSs, they actually have sufficient SINR to support an even higher-order modulation scheme to maintain better transmission capacity for provisioning IPTV services when compared to those SSs at the cell boundary of their home ONU-BS without much of interference (i.e. SS₃ and SS₄ in A3). This indicates that CCM not only effectively mitigates the inter-cell interference, but also promotes the ultimate gain of video multicasting in a large-scale deployment of multiple ONU- BSs in EPON-WiMAX access networks with wireless access and mobility.

Further Advantages

The cooperative coding applied by the present invention enables a receiver moving from the wireless coverage of an existing associated transmitter to a newly associated transmitter to seamlessly reconstruct the data of layer / as long as the minimum amount of video data of layer / can be obtained during the handover/movement across transmitters. Even without the use of MDC or any protection on each layer in the broadcast/multicast signal, the benefits of cooperative coding can still be achieved as long as layered broadcast/multicast transmission and the use of related STC are employed as described herein.

Additionally, there are several other alternative uses of the present invention for efficient and robust large-scale data broadcast or multicast services according to different implementations thereof. CCM can also be used for downlink transmission(s), for example for transmission of data from transmitted s) to receiver(s), in which the transmissions can be from transmitter(s) to receiver(s) via other receiver(s) or intermediary systems (i.e. multi-hop or relaying transmission). Similarly, CCM can also be used for uplink transmission(s), for example for transmission of data from receiver(s) to transmitted s), in which there are also single hop (i.e. multiple receivers transmitting data with CCM cooperatively to transmitter(s)) or multiple hop uplink transmissions (i.e., the data to transmitter(s) by CCM from cooperative receivers, which are obtained through other receivers also using CCM beforehand). These include the implementations provided in Table 2-1.

Table 2-1

An example of a multi-hop cooperative video transmission for multicast/broadcast to a single receiver is shown in FIG. 8. The BSi multicasts a video to two receivers (i.e., SSi and SS₂), which receive the same CCM signals with varying amount of video data according to their channel conditions during T_\. Both SSi and SS₂ may be equipped with forwarding functionalities use the invention to cooperatively forward their received CCM signals with or with any further signal processing to SS₃ during T₂ On the other side, BS₂ also multicasts the same video using the invention to three RSs (RSi, RS₂ and RS₃) during T\, which relays the CCM signal using the invention as well to two receivers (i.e., SS₇ and SS₃).

The result is the following transmission situations after T\ and T₂.

1. SSi only received cj MDC packets of layer / during T_\ and successfully forwarded c₂ MDC packets to SS₃ during T_2.

2. SS₂ only received d_\ MDC packets during T_\, and successfully forwarded d₂ MDC packets to SS₃ during T_2.

3. RS₄ received β_\ MDC packets from BS₂, and successfully forwarded e₂ MDC packets to SS₃.

Finally, SS₃ will still able to get a complete video data of layer / as long as c₂ + d₂+e₂ ≥ K_/ out of N MDC packets successfully received after T_\ and T₂.

In this example, the use of the invention of for multicast/broadcast to multiple receivers using multi-hop cooperative transmission is also realized (i.e., / BSs -^ / R/SSs -^ k SSs). BSi and BS2 transmit the CCM signal of the same video cooperatively to SS 1, SS₂ and RS₄, which cooperatively transmit the received CCM signals to SS₃ and SS₇ There are many other possible uses of the inventions based on the variations/combinations of the uses listed in Table 2-1. However, they generally share the same mechanisms to form cooperative coded transmissions using layered multicast/broadcast signals with/without protection on data in each layer using MDC or another protection code, in which some space- time coding is applied on each layered cooperative coded signal that coordinated across multiple BSs/RSs/SSs.

Additionally, it should be understood that the invention is not limited to fixed transmitters/base stations at fixed locations and the invention is not limited to free-space cooperative wireless communication, but also applicable to underwater cooperative wireless communications or any hybrid-medium of cooperative wireless communications.

REFERENCES

[1 ] Y. Huang, Y. -F. Chen, R. Jana, H. Jiang, M. Rabinovich, A. Reibman, B. Wei and Zhen Xiao, "Capacity analysis of MediaGrid: a P2P IPTV platform for fiber to the node (FTTN) networks", IEEE JSAC, vol. 25, no. 1, pp. 131 - 139, Jan. 2007.

[2] Gale Huang, "Experiences with PPLi ve", ACM SIGCOMM 2007, ACM SIGCOMM 2007, Peer-to-Peer Streaming and IP-TV Workshop, keynote presentation 1, August 27-31, 2007, [Available online May 19, 2008]: http://www.sigcomm.org/sigcomm2007/p2p- tv/Keynote-P2PTV-GALE_PPLIVE.ppt

[3] IEEE Standard 802.16-2004, "IEEE Standard for Local and Metropolitan Area Networks- Par 16:Air Interface for Fixed Broadband Wireless Access Systems," 2004.

[4] G. Shen, R. S. Tucker, and T. Chae, "Fixed Mobile Convergence (FMC) Architectures for Broadband Access: Integration of EPON and WiMAX," IEEE Communications Magazine, August 2007, pp.44-50.

[5] T. Jiang, W. Xiang, H. -H. Chen and Q. Ni, "Multicast Broadcast Services Support in OFDMA-Based WiMAX Systems",^^ Communications Magazine, vol. 45, no. 8, pp. 78-86, August 2007

[6] J. She, F. Hou, P.-H. Ho and L.-L. Xie, "IPTV over WiMAX: Key Success Factors, Challenges, and Solutions", IEEE Communications Magazine, vol. 45, no 8, pp.87-93, Aug. 2007.

[7] Y. S. Chan, J. W. Modestino, Q. Qu and X. Fan, "An End-to-End Embedded Approach for Multicast/Broadcast of Scalable Video over Multiuser CDMA Wireless Networks", IEEE Transactions on Multimedia, vol. 9, no. 3, pp. 655-667, Apr. 2007.

[8] V. K. Goyal, "Multiple description coding: Compression meets the network", IEEE Signal Processing Magazine, pp. 74-93, Sep 2001.

[9] P. A. Chou, H. J. Wang, and V. N. Padmanabhan, "Layered multiple description coding," Proc. PV 13th Int. Packet Video Workshop Nantes, Apr. 2003. [10] A. Albanese, J. Blomer, J. Edmonds, M. Luby, M. Sudan, "Priority encoding transmission", IEEE Trans. Information Theory, vol. 42, pp.1737-1744, Nov. 1996.

[1 1] I. D. Garcia, K. Sakaguchi, and K. Araki, "Cell Planning for Cooperative Transmission", in Proceedings IEEE Wireless Communication and Networking Conference (WCNC) 2008, April, 2008,, pp. pp. 1769 - 1774.

[12] J. She, X. Yu, F. Hou, P. -H. Ho, and E.-H. Yang, "A Framework of Cross-Layer Superposition Coded Multicast for Robust IPTV Services over WiMAX", in Proceedings IEEE Wireless Communication and Networking Conference (WCNC) 2008, April, 2008, pp. 3139 - 3144

[13] James She et ah, "Cooperative Coded Video Multicast for IPTV Services under EPON- WiMAX Integration", IEEE Communications Magazine, pp. 104-1 10, August 2008

[14] A. Sendonaris, E. Erkip, and B. Aazhang, "User cooperation diversity-Part I and Part II ," IEEE Trans. Commun., vol. 51 , pp. 1927-48, November 2003.

[15] V. Tarokh, H. Jafarkhani, and A. Calderbank, "Space-time block codes from orthogonal designs", IEEE Transactions on Information Theory, vol. 45, no. 5, pp. 14561467, July 1999.

[16] S. Alamouti, "A simple transmit diversity technique for wireless communications", /EEE Journal on Selected Areas in Communications, vol. 16, no. 8, pp. 14511458, October 1998.

[ 17] B. S. Mergen and A. Scaglione, "Randomized space-time coding for distributed cooperative communication", /EEE Transactions on Signal Processing, pp. 50035017, October 2007.

[18] H. Schwarz, D. Marpe, T. Wiegand, "Overview of the Scalable Video Coding Extension of the H.264/AVC Standard", IEEE Transactions on Circuits and Systems for Video Technology, pp. 1 1031 120, September 2007.

[19] P. Liu, Z. Tao, S. Narayanan, T. Korakis, and S. Panwar, "CoopMAC: A cooperative MAC for wireless LANs," /EEE Journal of Selected Topics In Communications, Volume 25, Issue 2,p.34O, February 2007 [20] O. Alay, T. Korakis, Y. Wang, E. Erkip, S. Panwar, "Layered Wireless Video Multicast using Omni-directional Relays", in Proceedings of IEEE ICASSP, 2008.

[21 ] O. Alay, Z. Xu, T. Korakis, Y. Wang, S. Panwar, "Implementing a Cooperative MAC Protocol for Wireless Video Multicast", in Proceedings of IEEE WCNC, Budapest, Hungary, 2009, available at http://vision.poly.edu/~ozgu/wcnc09.pdf

[22] B. Sirkeci-Mergen, A. Scaglione, and G. Mergen, "Asymptotic analysis of multi-stage cooperative broadcast in wireless networks", Joint special issue of IEEE Trans, on Information Theory and IEEE/ACM Trans. On Networking, June 2006.

[23] O. Alay, R. Ding, E. Erkip, Y. Wang and A. Scaglione, "Layered randomized cooperation for multicast", in Proceedings of IEEE 42^nd Annual Asilomar Conference on Signals, Systems and Computers , Pacific Grove, CA, October 2008 (invited).

[24] LAN MAN Standards Committee of the IEEE Computer Society, ANSI/IEEE Std 802.11, "Part 1 1 : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-speed Physical Layer Extension in the 2.4 GHz Band," IEEE 802.1 1 Standard, 1999.

[25] J. N. Laneman, D. N. C. Tse, and G. W. Wornell, "Cooperative diversity in wireless networks: Efficient protocols and outage behavior," IEEE IT, vol. 50, no. 12, p. 3062, December 2004.

[26] H. Jafarkhani, "Space-Time Coding: Theory and Practice", Cambridge University Press, 2005

[27] D. Gunduz and E. Erkip, "Source and channel coding for cooperative relaying," IEEE Transactions on Information Theory, Special Issue on Models, Theory, and Codes for Relaying and Cooperation in Communication Networks, vol. 53, no. 10, pp. 3453-3475, October 2007

[28] P. Liu, Z. Tao, Z. Lin, E. Erkip, and S. Panwar, " Cooperative wireless communications: A cross-layer approach," IEEE Wireless Communications, 13(4):8492, August 2006.

[29] F. Verde, T. Korakis, E. Erkip, and A. Scaglione, "On avoiding collisions and promoting cooperation: Catching two birds with one stone", in Proceedings of IEEE SPAWC, July 2008. [30] P. Liu, Y. Liu, T. Korakis, A. Scaglione, E. Erkip, S. Panwar, " Cooperative MAC for rate adaptive randomized distributed space-time coding", in Proceedings of IEEE GLOBECOM, New Orleans, Lousiana, November 2008.

[31 ] H. Y. Shutoy, D. Gunduz, E. Erkip and Y Wang, "Cooperative source and channel coding for wireless multimedia communications," IEEE Journal of Selected Topics In Signal Processing, Vol. 1 , Issue 2,p.295, Aug. 2007

Claims

1. A system for transmitting a data bitstream over a wireless network to one or more receivers, the system characterized by:

a. a scalable bitstream coding means for separating the data bitstream into a layered bitstream, each layer representing a different quality representation of the data bitstream;

b. a protection coding means for applying protection coding to the layered bitstream to create a protected bitstream;

c. a superposition coding means for applying one or more different modulation schemes to the protected bitstream to create a modulated bitstream; and

d. a coding means for cooperative transmission operable to apply one or more orthogonal codes at a plurality of transmitters for cooperatively transmitting the modulated bitstream to the one or more receivers.

2. The system as claimed in claim 1, characterized in that the coding means for cooperative transmission applies space-time coding to the modulated bitstream.

3. The system as claimed in claim 1, characterized in that the scalable bitstream coding means applies multiple description coding to each layer, wherein the degree of coding applied to relatively lower quality representations of the data is less than the degree of coding applied to relatively higher quality representations of the data.

4. The system as claimed in claim 3, characterized in that the coding is a redundancy coding.

5. The system as claimed in claim 1, characterized in that at least two of the transmitters are operable to transmit the modulated bitstreams to a particular location and the coding means for cooperative transmission is operable to provide additive power to at least one of the one or more receivers at the particular location.

6. The system as claimed in claim 1 , characterized in that the one or more receivers include a cooperative transmission decoder, multi-resolution demodulator, protection decoder and scalable bitstream decoder, the one or more receiver operable to produce a representation of the data bitstream.

7. The system as claimed in claim 1 , characterized in that the one or more receiver is operable to produce a representation of the data bitstream when it moves from one of the transmitter's coverage area to another of the transmitter's coverage area.

8. The system as claimed in claim 1, characterized in that the wireless network is an integrated EPON-WiMAX network.

9. A method for transmitting a data bitstream over a wireless network to one or more receivers, the method characterized by:

a. separating the data bitstream into a layered bitstream, each layer representing a different quality representation of the data bitstream;

b. applying protection coding to the layered bitstream to create a protected bitstream;

c. applying one or more different modulation schemes to the protected bitstream to create a modulated bitstream; and

d. applying one or more orthogonal codes to a plurality of transmitters for cooperatively transmitting the modulated bitstream to the one or more receivers.

10. The method as claimed in claim 9, characterized in that the orthogonal codes are provided by space-time coding.

1 1. The method as claimed in claim 9, characterized in that the layered bitstream is provided by a multiple description coding for applying a coding to each layer, wherein the degree of coding applied to relatively lower quality representations of the data is less than the degree of coding applied to relatively higher quality representations of the data.

12. The method as claimed in claim 1 1, characterized in that the coding is a redundancy coding.

13. The method as claimed in claim 9, characterized in that at least two of the transmitters are operable to transmit the modulated bitstreams to a particular location and the transmitters applying the orthogonal codes provides additive power to the modulated bitstream received by at least one of the one or more receivers at the particular location.

14. The method as claimed in claim 9, characterized in that the one or more receivers include a cooperative transmission decoder, multi-resolution demodulator, protection decoder and scalable bitstream decoder, the one or more receiver operable to produce a representation of the data bitstream.

15. The system as claimed in claim 9, characterized in that the one or more receiver is operable to produce a representation of the data bitstream when it moves from one of the transmitter's coverage area to another of the transmitter's coverage area.

16. The method as claimed in claim 9, characterized in that the wireless network is an integrated EPON-WiMAX network.