HK1148129B - Method and apparatus for minimizing co-channel interference by scrambling - Google Patents

Description

Method and apparatus for minimizing co-channel interference by scrambling

The present application is a divisional application of the inventive patent application having application number 200580026710.0, 26/5/2005 entitled "method and apparatus for minimizing co-channel interference by scrambling".

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from earlier filing days of U.S. provisional application having a sequence number of 60/583,410 entitled "screening of Physical Layer Header and Pilot Symbol in DVB-S2to Reduce Co-Channel Interference" filed on 28/6/2004 and U.S. provisional application having a sequence number of 60/585,654 entitled "screening of Physical Layer Header and Pilot Symbol in DVB-S2to Reduce Co-Channel Interference" filed on 6/7/2004; the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to communication systems, and more particularly to combating signal interference.

Background

Broadcast systems have included a need for high quality transmissions that digital techniques make possible. The digital revolution has changed the delivery of broadband services including audio and video programming and data transmission. Satellite communication systems have emerged as a viable solution for supporting such broadband services. Thus, power and bandwidth efficient modulation and coding is highly advantageous for satellite communication systems to provide reliable communication over noisy communication channels. Receiver performance is negatively affected by co-channel interference. This interference occurs mainly due to frequency reuse when the spectrum allocation of frequencies is limited and expensive. In practical applications, co-channel interference may result from transmissions from other system operators, satellites operating in adjacent orbital locations, or other spot beams in a spot beam satellite system.

Traditionally, the negative effects of co-channel interference have been minimized by redesigning the frequency allocation or changing (by upgrading) the transmission facilities in order to limit the spreading of the signal. These methods require significant engineering investment (assuming that a technical solution is possible); this entails a great cost.

Therefore, a need exists for a communication system that minimizes co-channel interference without requiring significant system redesign.

Disclosure of Invention

These and other needs are addressed by the present invention, which provides a method for minimizing co-channel interference in digital broadcast and interactive systems. It has been recognized that: the cross-correlation between co-channel frames is periodic in nature. Each of these frames includes a header and a pilot sequence for synchronizing the carrier phase and carrier frequency. The non-header portion of the frame is scrambled according to respective different scrambling sequences to minimize co-channel interference. According to one embodiment of the invention, different initialization seeds are provided to the Gold sequence generator for each co-channel to generate different scrambling sequences. The above arrangement advantageously reduces the effect of co-channel interference and thereby improves receiver performance.

According to an aspect of an embodiment of the present invention, a method for minimizing co-channel interference in a communication system is disclosed. The method comprises the following steps: the first co-channel is assigned a first scrambling sequence associated with a header or pilot sequence of the first frame. The method further comprises the following steps: a second co-channel adjacent to the first co-channel is assigned a second scrambling sequence associated with a header or pilot sequence of the second frame. The non-header portion of the frame is scrambled according to respective different scrambling sequences.

According to another aspect of an embodiment of the present invention, an apparatus for minimizing co-channel interference in a communication system is disclosed. The apparatus includes a scrambler configured to assign a first scrambling sequence to a first co-channel, the first scrambling sequence associated with a header or pilot sequence of a first frame. The scrambler assigns a second scrambling sequence to a second co-channel adjacent to the first co-channel, the second scrambling sequence being associated with a header or pilot sequence of a second frame. The non-header portion of the frame is scrambled according to the respective scrambling sequence.

According to another aspect of an embodiment of the present invention, a method for communicating in a wireless communication system is disclosed. The method comprises the following steps: the plurality of frames are transmitted via different communication channels established over the wireless communication system. The communication channel is an adjacent co-channel. Each frame includes a header and a pilot sequence for synchronizing a carrier phase and a carrier frequency, and non-header portions of the frame are scrambled according to respective different scrambling sequences so as to minimize interference between co-channels.

According to another aspect of an embodiment of the present invention, an apparatus for communicating in a wireless communication system is disclosed. The apparatus includes a transmitter configured to transmit a plurality of frames via different communication channels established on the wireless communication system, wherein the communication channels are adjacent co-channels. Each frame includes a header and a pilot sequence for synchronizing a carrier phase and a carrier frequency, and non-header portions of the frame are scrambled according to respective different scrambling sequences so as to minimize interference between co-channels.

According to another aspect of an embodiment of the present invention, a method for communicating in a wireless communication system is disclosed. The method comprises the following steps: a plurality of frames are received via different communication channels established over the wireless communication system. The communication channel is an adjacent co-channel. Each frame includes a header and a pilot sequence for synchronizing a carrier phase and a carrier frequency, and non-header portions of the frame are scrambled according to respective different scrambling sequences so as to minimize interference between co-channels.

According to yet another aspect of an embodiment of the present invention, an apparatus for communicating in a wireless communication system is disclosed. The apparatus includes a receiver configured to receive a plurality of frames via different communication channels established on the wireless communication system, wherein the communication channels are adjacent co-channels. Each frame includes a header and a pilot sequence for synchronizing a carrier phase and a carrier frequency, and non-header portions of the frame are scrambled according to respective different scrambling sequences so as to minimize interference between co-channels.

Other aspects, features, and advantages of the present invention will become more apparent from the following detailed description, simply by illustrating a number of specific embodiments and implementations, including the best mode contemplated for carrying out the present invention. The invention is capable of other and different embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

Drawings

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

fig. 1 is a schematic diagram of a digital broadcasting system capable of minimizing co-channel interference according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an exemplary transmitter for use in the digital transmission equipment of the system of FIG. 1;

FIG. 3 is a schematic diagram of an exemplary digital modem in the system of FIG. 1;

FIG. 4 is a schematic diagram of an exemplary frame structure for use in the system of FIG. 1;

FIGS. 5A and 5B are schematic diagrams of a scrambler for isolating co-channel interference and a Gold sequence generator for outputting Gold codes used to construct scrambling codes, respectively, according to various embodiments of the present invention;

FIG. 6 is a diagram illustrating the periodic nature of cross-correlation between co-channel frames according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of an exemplary Gold sequence generator for use in the scrambler of FIG. 6;

FIG. 8 is a flow diagram of a process for generating different physical layer sequences, according to an embodiment of the invention;

FIG. 9 is a flow diagram of a process for generating a scrambled physical layer header according to an embodiment of the present invention;

FIGS. 10 and 11 are tables illustrating a worst-case cross-correlation of pilot segments for each pair of co-channels used to determine an initialization seed for the m-generator of FIG. 7; and

fig. 12 is a schematic diagram of a hardware platform that may perform various processes for isolating co-channel interference, according to an embodiment of the invention.

Detailed Description

An apparatus, method and software for reducing co-channel interference in digital broadcast and interactive systems are described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention.

Fig. 1 is a schematic diagram of a digital broadcasting system capable of minimizing co-channel interference according to an embodiment of the present invention. The digital communication system 100 includes a digital transmission facility 101 for generating signal waveforms for broadcast over a communication channel 103 to one or more digital modems 105. According to one embodiment of the present invention, communication system 100 is a satellite communication system that supports, for example, audio and video broadcast services as well as interactive services. Interactive services include, for example, Electronic Program Guides (EPGs), high speed internet access, interactive advertising, telephony, and email services. These interactive services may also include television services such as Pay Per View (PayPer View), TV Commerce (TV Commerce), Video On Demand (Video On Demand), NearVideo On Demand (near Video On Demand), and Audio On Demand (Audio On Demand) services. In this case, the modem 105 is a satellite modem.

In broadcast applications, the continuous mode modem 105 is widely used. For synchronization (e.g., carrier phase and carrier frequency), codes that work well in low signal-to-noise ratio (SNR) environments collide with these modems. Physical layer headers and/or pilot symbols may be used for such synchronization. An important consideration for system performance is therefore co-channel interference of the physical layer header and/or pilot symbols. Such interference can degrade receiver performance since the physical layer header and/or pilot are used to acquire and/or track carrier phase, carrier frequency.

Conventional digital broadcasting systems (not shown) require the use of additional training symbols in the frame structure for their synchronization processing in addition to the normal overhead bits. An increase in overhead is particularly required when the signal-to-noise ratio (SNR) is low; this is typical when high performance codes are used in conjunction with high order modulation. Traditionally, continuous mode modems use a feedback control loop to acquire and track carrier frequency and phase. In such a synchronization process, the FEC (forward error correction) -encoded data field containing known data symbols, e.g. the preamble of a block code, is simply ignored. This conventional approach, which is based entirely on a feedback control loop, is prone to strong Radio Frequency (RF) phase noise and thermal noise, resulting in high cycle slip rates (slips rates) and error floor (error floor) for overall receiver performance. Thus, in addition to a limited acquisition range and long acquisition time, the increased overhead burdens these methods in terms of training symbols for specific performance targets. Furthermore, these conventional synchronization techniques rely on a specific modulation scheme, thereby hindering flexibility in the use of the modulation scheme.

In the system 100 of fig. 1, the modem 105 achieves carrier synchronization by examining the preamble and/or Unique Word (UW) embedded in the broadcast data frame structure (shown in fig. 4), thereby reducing the use of overhead that is specifically designated for training purposes. The digital modem 105 is described more fully below with reference to fig. 3.

In this discrete communication system 100, a transmission facility 101 generates a discrete set of possible messages representing media content (e.g., audio, video, textual information, data, etc.); each possible message has a corresponding signal waveform. These signal waveforms are attenuated or altered by the communication channel 103. To combat the noisy channel 103, the transmission facility 101 uses a Low Density Parity Check (LDPC) code.

The LDPC code generated by the transmission facility 101 enables high speed implementation without incurring any performance penalty. These constructed LDPC codes output from the transmission facility 101 avoid assigning a small number of check nodes to bit nodes that have been vulnerable to channel errors due to the modulation scheme (e.g., 8 PSK). Such LDPC codes have parallelizable decoding processes (unlike turbo codes) that advantageously include simple operations such as addition, comparison, and table lookup. Moreover, well-designed LDPC codes do not exhibit any evidence of error floor.

According to one embodiment of the invention, the transmission facility 101 generates LDPC codes based on a parity check matrix (which facilitates efficient memory access during decoding) for communication with the satellite modem 105 using a relatively simple encoding technique explained below in fig. 2.

Fig. 2 is a schematic diagram of an exemplary transmitter for use in the digital transmission facility of the system of fig. 1. The transmitter 200 is equipped with an LDPC encoder 203 for accepting an input from an information source 201 and outputting an encoded stream with higher redundancy suitable for error correction processing at the receiver 105. The information source 201 produces k signals from the discrete alphabet X. The LDPC code is specified using a parity check matrix. Encoding LDPC codes, on the other hand, typically requires specifying a generator matrix. Even if the generator matrix can be obtained from the parity check matrix using gaussian elimination, the resulting matrix is no longer sparse and storing a large generator matrix can be complicated.

The encoder 203 generates the signal from the alphabet Y to the modulator 205 using a simple coding technique that uses only the parity check matrix by imposing a structure on the parity check matrix. Specifically, the constraint is placed on the parity check matrix by constraining certain portions of the matrix to triangles. This limitation results in negligible performance loss and, therefore, an attractive balance is established. The construction of such Parity Check matrices is more fully described in a copending patent application entitled "method System for Providing Low Density Parity Check (LDPC) Encoding," filed on 3/7/2003, attorney docket number PD-203016; Ser. Nos. 10/613, 823, the entire contents of which are incorporated herein by reference.

The modulator 205 maps the encoded message from the encoder 203 to signal waveforms that are sent to the transmit antenna 207, which transmit antenna 207 transmits the waveforms via the communication channel 103. The encoded message is thus modulated and distributed to the transmit antennas 207. The transmission from the transmit antenna 207 propagates to the digital modem as described below. In the case of a satellite communication system, the transmission signal from the antenna 207 is relayed via a satellite. Transmitter 200 also includes a scrambler 209 for altering symbols used for transmission in order to minimize co-channel interference, as described more fully below.

Fig. 3 is a schematic diagram of an exemplary digital modem in the system of fig. 1. The digital modem 300, which is a modulator/demodulator, supports transmission and reception of signals from the transmitter 200. According to one embodiment of the invention, modulator 300 has a front end module 301 that provides filtering and symbol timing synchronization of the LDPC coded signal received from antenna 303; a carrier synchronization module 302 that provides frequency and phase acquisition and tracking of the signal output from the front end module 301. The demapper 305 performs demapping of the received signal output from the carrier synchronization module 302. After demodulation, the signal is forwarded to LDPC decoder 307, which attempts to reconstruct the original source message by generating message X'.

On the transmitting side, the modem 300 encodes an input signal using the LDPC encoder 309. The encoded signal is then modulated by a modulator 311, which modulator 311 may use a variety of modulation schemes — for example, Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8PSK, 16 Amplitude Phase Shift Keying (APSK), 32APSK, higher order Quadrature Amplitude Modulation (QAM), or other higher order modulation schemes.

Fig. 4 is a schematic diagram of an exemplary frame structure for use in the system of fig. 1. By way of example, an LDPC encoded frame 400 is shown that may support, for example, satellite broadcast and interactive services. Frame 400 includes a physical layer header (denoted "PLHEADER") 401 and occupies one slot, as well as other slots 403 for data or other payloads. Further, according to one embodiment of the invention, frame 400 utilizes pilot block 405 to assist in synchronizing carrier phase and frequency. Note that the pilot block 405 is optional, and the pilot block 405 is inserted via a pilot insertion process. Although pilot block (or pilot sequence) 405 representing a Unique Word (UW) is shown after 16 time slots 403, pilot block 405 may be inserted anywhere along frame 400.

In an exemplary embodiment, the pilot insertion process inserts pilot blocks every 1440 symbols. In this scenario, the pilot block includes 36 pilot symbols. For example, in physical layer frame 400, a first pilot block is therefore inserted 1440 symbols after the plan, a second pilot block is inserted 2880 symbols after, and so on. If the pilot block position coincides with the start of the next ploader, no pilot block is inserted. The above-described pilot insertion process is described in further detail in a co-pending application entitled "Method and Apparatus for providing Carrier Synchronization in Digital broadcasting and Interactive Systems" (application No. 10/842,325, 5/10/2004), which is incorporated herein in its entirety.

The carrier synchronization module 302 (fig. 3) according to an embodiment of the present invention uses the ploader 401 and/or the UW 405 for carrier frequency and phase synchronization. As previously described, FEC encoded data containing known data symbols (e.g., PLHEADER 401) is conventionally ignored in continuous mode modems. That is, the PLHEADER 401 and/or the UW 405 are used for carrier synchronization, i.e., to assist in frequency acquisition and tracking operations, as well as phase tracking loops. Thus, PLHEADER 401 and UW 405 are considered "training" or "pilot" symbols and, individually or collectively, constitute a training block.

For 8PSK modulation, the pilot sequence 405 is a 36 symbol long segment (where each symbol isI.e., 36 symbols (PSK). In frame 400, pilot sequence 405 may be inserted after 1440 symbols of data. In this scenario, PLHEADER 401 may have 64 possible formats depending on the modulation, coding, and pilot configuration.

To mitigate the effects of co-channel interference, the non-header portion 407 of the frame 400 is scrambled. The scrambling process is further explained with reference to fig. 5A, 5B and 8, 9. As used herein, the scrambled pilot sequence is also denoted as the "pilot segment" of the frame 400. Furthermore, although frame 400 exhibits a frame structure for 8 PSK-modulation, a QPSK-modulated frame may contain 22 pilots when transmitted in long frame mode (e.g., 64800 data bits/frame).

Although the frame 400 is described with reference to a structure that supports satellite broadcast and interactive services (and is compatible with the Digital Video Broadcast (DVB) -S2 standard), it should be appreciated that: the carrier synchronization technique of the present invention can be applied to other frame structures.

Fig. 5A is a schematic diagram of a scrambler for isolating co-channel interference in accordance with an embodiment of the present invention. According to one embodiment of the invention, the scrambling code is a complex sequence that can be constructed from Gold codes. That is, the scrambler 209 generates the scrambling sequence rn (i). Table 1 defines how the scrambling sequence rn (i) scrambles the frames using the scrambler 209 according to the scrambler logic of fig. 7. In particular, table 1 shows a mapping of input symbols to output symbols based on the output of the scrambler 209.

Rn(i)	Input (i)	Output (i)
			0	1+jQ	1+jQ
1	1+jQ	-Q+j1
			2	1+jQ	-1-jQ
3	1+jQ	Q-j1

TABLE 1

By using different seeds for either of the two m-sequence generators, different Gold sequences can be generated. By using different seeds for different services, mutual interference may be reduced.

In broadcast mode, the 90 symbol physical layer header 401 may remain unchanged for a particular physical channel. The Gold sequence is rearranged at the beginning of each frame and, therefore, the scrambled pilot is also periodic with a period equal to the frame length. Since the information carrying the data in the frame changes and appears random, the co-channel interference is random and reduces the operating signal-to-noise ratio. However, due to the time-varying nature of the physical layer header 401 and pilot block 405, there is a bias for the receiver carrier and phase estimates from these pilots and physical layer headers for such acquisition and tracking. This will degrade performance in addition to the signal to noise ratio degradation associated with random data.

The scrambler 209 utilizes different scrambling sequences (n total) to further isolate co-channel interference. Each scrambling sequence or pilot sequence corresponds to a different seed n. By way of example, 17 possible configurations are provided, as shown in table 2 below. In each configuration, one scrambling sequence is provided for the physical layer header and one scrambling sequence is provided for the pilot. Different pilots are assigned according to different seeds of the Gold sequence.

Fig. 5B provides a schematic diagram of a Gold sequence generator for outputting Gold codes used to construct scrambling codes, according to an embodiment of the invention. As shown, the Gold sequence generator 500 uses two pseudo-noise (PN) sequence generators 501, 503 to generate a "preferred pair" of sequences. The "preferred pair" may be specified by a "preferred polynomial" (as seen in the scrambler of fig. 7). The outputs of these PN sequence generators 501, 503 are fed to XOR logic 505, which XOR logic 505 performs an XOR function on the output sequences to produce Gold sequences. The Gold sequence generator 500 generates Gold sequences from large sequence classes that exhibit good periodic cross-correlation properties. Using period N-2ⁿ-1 to define a Gold sequence by a given pair of sequences u and v; such a pair is called a "preferred pair". The set of Gold sequences G (u, v) is defined as follows:

equation 1

Where T represents an operator that circularly shifts the vector one position to the left, andrepresenting modulo-2 addition. Note that: g (u, v) contains N +2 sequences of period N. The Gold sequence has the following properties: the cross-correlation between any two Gold sequences, or a shifted version thereof, takes one of 3 values-t (n), -1, or t (n) -2, where:

equation 2

Returning to the scrambler 209, in operation, a different seed or physical layer sequence is used for the "adjacent co-channel". The scrambling mechanism of the scrambler 209 advantageously reduces the signaling by correlating between the physical layer signaling and different seeds representing different Gold sequences one by one. Table 2 lists the selection of scrambling sequences for the physical layer header in 8-ary format.

000000000000000000000000000000017441442073372365611356321532265426356443536276670211411740252227554465164204771634274377776172163477102134531155722252723677114643600327625322063065530630226523726003613144773627414501457322433557672435620361436023561273755661226751405141152764667421361462275664347537765716133572231436421733137254475506033002140572621247123361436624712423275014200660305571546402134245534407404410536306306365041101701165512164201315417456000231306236305251032641413260452506362306462000351741

TABLE 2

It is assumed that the data is independent in the co-channel. Thus, the co-channel interference includes only items corresponding to cross-correlations between pilot bands of the channel. The data of one channel is also uncorrelated with the pilot segments on the other channels. Depending on the degree of overlap, the correlation may be complete or partial. The correlation C of the pilot bands x (n) and y (n) is shown in equation 3_XY(n), wherein the sum is based on the number of overlapping symbols.

Equation 3

Furthermore, it is important to note that these cross-correlations are periodic in nature; that is, they are reproduced at a frame rate. As shown in fig. 6, frames 601, 603 associated with co-channel 1 are simply shifted with respect to frames 605, 607 of co-channel 2.

If the co-channels use the same seed and are perfectly aligned (with aligned frame boundaries), then the cross-correlation of their pilot segments yields the following relationship:

C_XY(0)＝A_xA_ye^jφequation 4

Wherein A is_xAnd A_yAre the amplitudes of vectors x (k) and y (k), respectively, and φ is the phase difference between vectors x (k) and y (k). This correlation has the effect of rotating the desired user signal, resulting in severe interference.

Fig. 7 is a schematic diagram of an exemplary Gold sequence generator for use in the scrambler of fig. 6. Interference may be reduced by using different Gold sequences for the co-channels, i.e., different initialization seeds for each of the co-channels. In this example, Gold sequence generator 700 utilizes a preferred polynomial 1+ X⁷+X¹⁸And 1+ Y⁵+Y⁷+Y¹⁰+Y¹⁸. Continuing with the example of fig. 5, to maintain 17 co-channels, in an exemplary embodiment of the invention, the seeds in tables 3 and 4 may be programmed into m-sequence generator 701. The polynomial is initialized as follows: x (0) ═ 1, and X (1) ═ X (2) · X (17) ═ 0; and Y (0) ═ Y (1) ═ X (2) · X (17) ═ 1. The Gold code sequence corresponding to the initialization is also listed in table 3Number "n".

According to one embodiment of the invention, the seed is generated by using a suboptimal search algorithm that minimizes the worst cross-correlation between each pair of co-channel pilot segments.

TABLE 3

TABLE 4

The worst-case correlations between any two of the co-channels listed in tables 3 and 4 are given in fig. 10 and 11, respectively. The maximum cross-correlation is seen in fig. 10 to be-2.78 dB (highlighted in bold). For fig. 11, this maximum cross-correlation occurs at-2.92 dB. It can be observed that: although the Gold sequence itself has good cross-correlation properties, the pilot segment may exhibit poor cross-correlation properties. This is due to the fact that: these segments are only 36 symbols long and the seed selection process is subject to the worst cross-correlation constraint.

The scrambling process in fig. 8 and 9 is now further explained.

Fig. 8 is a flow diagram of a process for generating different physical layer sequences, according to an embodiment of the invention. In step 801, different initialization seeds are assigned to the respective co-channels. Next, a Gold sequence is generated based on the seed, via step 803. Then, in step 805, a scrambling sequence is constructed from the Gold sequences for each different service. In step 807, the physical layer sequence is output by scrambler 209 (fig. 2).

Fig. 9 is a flow diagram of a process for generating a scrambled physical layer header according to an embodiment of the present invention. In step 901, transmitter 200 (of fig. 2) receives input symbols associated with a physical layer header or pilot sequence. In step 903, the transmitter maps the input symbols according to the scrambling sequence generated by the scrambler 209. An output symbol is then generated, via step 905. The transmitter then outputs a frame with the scrambled physical sequence and/or the scrambled pilot sequence (step 907).

FIG. 12 illustrates exemplary hardware upon which embodiments in accordance with the invention may be implemented. Computing system 1200 includes a bus 1201 or other communication mechanism for communicating information, and a processor 1203 connected to bus 1201 for processing the information. The computing system 1200 also includes a main memory 1205, such as a Random Access Memory (RAM) or other dynamic storage device, coupled to the bus 1201 for storing information and instructions to be executed by the processor 1203. The main memory 1205 may also be used for temporarily storing variables or other intermediate information during execution of instructions by the processor 1203. Computing system 1200 may further include a Read Only Memory (ROM)1207 or other static storage device coupled to bus 1201 for storing static information and instructions for processor 1203. A storage device 1209, such as a magnetic disk or optical disk, is coupled to the bus 1201 for persistently storing information and instructions.

Computing system 1200 may be connected via bus 1201 to a display 1211, such as a liquid crystal display or active matrix display, for displaying information to a user. An input device 1213, such as a keyboard including alphanumeric and other keys, may be connected to the bus 1201 for communicating information and command selections to the processor 1203. The input device 1213 may include a cursor control, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processor 1203 and for controlling cursor movement on the display 1211.

The processes of fig. 8 and 9 may be provided by the computing system 1200 in response to the processor 1203 executing a set of instructions contained in main memory 1205, according to one embodiment of the invention. Such instructions may be read into main memory 1205 from another computer-readable medium, such as storage device 1209. Execution of the arrangement of instructions contained in the main memory 1205 causes the processor 1203 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be used to execute the instructions contained in main processor 1205. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the invention. In another example, reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) may be used, where the functional and connection layout of its logic gates is customizable at runtime, typically by programming memory look-up tables. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.

The computing system 1200 also includes at least one communication interface 1215 coupled to the bus 1201. Communication interface 1215 provides a two-way data communication by way of a connection to a network link (not shown). Communication interface 1215 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. In addition, communication interface 1215 can include peripheral interface devices such as a Universal Serial Bus (USB) interface, a PCMCIA (personal computer memory card International Association) interface, and the like.

The processor 1203 may execute the code being received via the communication interface 1215 and/or store the code in the storage device 1209 or other non-volatile storage for later execution. In this manner, computing system 1200 may obtain application program code in the form of a carrier wave.

The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor 1203 for execution. Such a medium may take many forms, including but not limited to, non-volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device 1209. Volatile media includes dynamic memory, such as main memory 1205. Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1201. Transmission media can also take the form of acoustic, optical, or electromagnetic waves, such as those generated during Radio Frequency (RF) and Infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.

Various forms of computer readable media may be involved in providing instructions to a processor for execution. For example, the instructions for carrying out at least part of the present invention may initially be borne on a magnetic disk of a remote computer. In this scenario, the remote computer loads the instructions into main memory and sends the instructions over a telephone line using a modem. A modem of a local system receives the data on the telephone line and uses an infrared transmitter to convert the data to an infrared signal and transmit the infrared signal to a portable computing device, such as a Personal Digital Assistant (PDA) or a laptop. An infrared detector on the portable computing device receives the information and instructions carried by the infrared signal and places the data on a bus. The bus transfers the data to main memory, from which the processor retrieves and executes the instructions. The instructions received by main memory are optionally stored on storage device either before or after execution by processor.

Accordingly, various embodiments of the present invention provide a method for minimizing co-channel interference in digital broadcasting and interactive systems. It should be appreciated that: the cross-correlation between co-channel frames is periodic in nature. Each of these frames includes a header and a pilot sequence for synchronizing the carrier phase and carrier frequency. The non-header portion of the frame is scrambled according to respective different scrambling sequences to minimize co-channel interference. According to one embodiment of the invention, different initialization seeds are provided to the Gold sequence generator for each co-channel to generate different scrambling sequences. The above arrangement advantageously reduces the effect of co-channel interference and thus improves receiver performance.

While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.

Claims (13)

1. A method of minimizing interference between a plurality of adjacent co-channels in a communication system, wherein each frame in the plurality of adjacent co-channels includes a header and a payload portion, the method comprising:

allocating a first scrambling sequence to a header of a frame of a first channel of the plurality of adjacent co-channels; and

allocating a second scrambling sequence to a header of a frame of a second channel of the plurality of adjacent co-channels, the second channel being different from the first channel, wherein a seed for the first scrambling sequence and a seed for the second scrambling sequence are both selected from table a or both selected from table B, wherein a seed for the first scrambling sequence is different from a seed for the second scrambling sequence:

TABLE A

TABLE B

And wherein respective non-header portions of the plurality of frames are scrambled according to respective different scrambling sequences assigned to the respective headers.

2. The method of claim 1, further comprising: the seed is selected so as to minimize the worst cross-correlation case.

3. The method of claim 1, wherein the header is used for at least one of acquiring a carrier phase and acquiring a carrier frequency.

4. The method of claim 1, wherein the header is used to at least one of track a carrier phase and track a carrier frequency.

5. The method of claim 1, wherein each frame further comprises a pilot sequence.

6. The method of claim 5, wherein the pilot sequence is used to at least one of acquire a carrier phase and acquire a carrier frequency.

7. The method of claim 5, wherein the pilot sequence is used to at least one of track a carrier phase and track a carrier frequency.

8. The method of claim 1, further comprising:

transmitting frames in the plurality of adjacent co-channels according to a modulation scheme, the modulation scheme including at least one of binary phase shift keying, quadrature phase shift keying, 8-ary phase shift keying, 16-ary amplitude phase shift keying, 32-ary amplitude phase shift keying, and high order quadrature amplitude modulation.

9. The method of claim 1, further comprising:

the frame in the first channel is modulated in a first modulation scheme and the frame in the second channel is modulated in a second modulation scheme.

10. The method of claim 1, wherein each frame further comprises information encoded according to a low density parity check coding scheme.

11. An apparatus for communicating in a wireless communication system, comprising:

a receiver configured to receive a plurality of frames via a plurality of adjacent co-channels in a communication system, wherein each frame in the plurality of adjacent co-channels comprises a header and a payload portion; wherein a non-header portion of a frame in each of the plurality of adjacent co-channels is scrambled with a different scrambling sequence, wherein seeds for the different scrambling sequences are different, all scrambling seeds are selected from table a or all scrambling seeds are selected from table B:

TABLE A

Table B.

12. The apparatus of claim 11, wherein each frame has a structure compliant with a digital video broadcast standard.

13. The apparatus of claim 11, wherein each frame further comprises information encoded according to a low density parity check coding scheme.