Information
-
Patent Grant
-
6463074
-
Patent Number
6,463,074
-
Date Filed
Wednesday, June 14, 200024 years ago
-
Date Issued
Tuesday, October 8, 200221 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Olms; Douglas
- Pizzaro; Ricardo M.
Agents
- Hamilton, Brook, Smith & Reynolds, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 370 442
- 370 443
- 370 444
- 370 431
- 370 321
- 370 337
- 370 347
- 370 322
- 370 324
- 370 314
- 370 329
- 370 508
- 370 203
- 370 208
- 370 345
- 370 458
- 370 450
- 370 348
- 370 507
- 370 349
- 370 346
- 714 752
- 714 701
- 714 758
- 714 761
- 714 762
-
International Classifications
-
Abstract
A technique for a time division multiplex system in which access to shared broadcast communication media is granted on a demand basis. Particular connections are assigned slot times at the transmitter based on demand. However, no specific information regarding the assignment of time slots need be communicated to the receivers. The transmit side employs a forward error correction technique followed by multiplication by a cover sequence unique to each connection. All receivers listen to the broadcast transmission channel all of the time. The receiver assigned to each connection decodes the signals in such a manner that only the receiver with the correct cover sequence assigned to a particular connection will successfully decode the data associated with that connection. Data frames that fail the forward error correction process are discarded, and only those frames which are successfully decoded are passed up to a higher layer. The occurrence of an erroneously received frame is not necessarily always reported to the transmit side of the connection; only a packet level error indication is made. In this way, information containing time slot assignment need not be communicated between the transmitter and receiver, and yet data will be correctly received.
Description
BACKGROUND
Continued growth in the electronics and computer industries, and indeed growth in the economy in general, is increasingly attributed to the demand for access to the Internet and myriad of services and features that it provides. The proliferation in the use of computing equipment, both of the conventional desk top variety as well as of the portable variety, including laptop computers, hand-held Personal Digital Assistants (PDAs), Internet enabled cellular telephones and other access devices have resulted in a corresponding increase in demand for network infrastructure.
The access points into the Internet are, however, mostly provided via communication systems that were originally intended for carrying non-data traffic. For example, the Public Switched Telephone Network (PSTN) is still heavily used as a dial-up access point for many home and personal users. Although there are emerging various standards that provide higher speed access points, these emerging technologies, as well as older high speed technologies such as TI and/or fractional TI services still make use of the telephone network. The telephone network was, unfortunately, optimized to carry voice traffic as opposed to data traffic. In particular, these networks were intended to support continuous analog communications, as compared to the digital communication protocols needed for Internet packet-oriented communications.
For example, voice grade services typically require access to a communication channel bandwidth of approximately 3 kilohertz (kHz). While techniques do exist for communicating data over such radio channels at a rate of 9.6 kilobits per second (kbps), such low bandwidth channels do not lend themselves directly to efficient transmission of data at the typical rates of 56.6 kbps or higher that are now commonly expected.
In addition, the very nature of Internet traffic itself is different from the nature of voice traffic. Voice communication requires a continuous duplex connection, that is, a user at one end of a connection expects to be able to transmit and receive to a user at the other end of a connection continuously, while at the same the user at the other end is also transmitting and receiving.
Usage patterns of the Internet are also quite different from voice communications. For example, consider that access to Web pages over the Internet in general is burst-oriented. Typically, the user of a remote client computer first specifies the address of a Web page to a browser program. The browser program at the client computer then sends the request as a Transmission Control Protocol (TCP)/Internet Protocol (IP) message packet, which is typically about 1000 bytes in length, to a network Web server. The Web server then responds by sending the content of the requested Web page, which may include anywhere from approximately 10 kilobytes to several megabytes of text, image, audio or video data. Because of delays inherent in the network, and because the Internet is such a vast interconnected mesh of networks, users experience delays of several seconds or more for the requested web page to be routed to them. The user may thereafter spend several seconds or even several minutes reading the contents of the page before specifying a next page to be downloaded.
The result is that a typical Internet connection remains idle for a relatively long period of time. However, once a request is made, the user expects the information to be transmitted to the client at a relatively rapid rate. An additional difficulty is provided in wireless access systems in that there are typically many more potential users or subscribers than the available number of physical radio channels. Therefore, making wireless channels available only on an instantaneous “as needed” basis makes sense, and indeed is a requirement if wireless data transfer services are to efficiently operate. Thus, dynamic traffic channel allocation schemes are one way to increase the efficiency wireless data communication systems in an effort to more efficiently utilize available channel resources.
Some type of demand-based multiple access technique is therefore typically required to make maximum use of the available wireless channels. Multiple access is often provided in the physical layer, such as by Frequency Division Multiple Access (FDMA) or by schemes that manipulate the radio frequency signal such as Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA). In any event, the nature of the radio spectrum is such that it is a medium that is expected to be shared. This is quite dissimilar to the traditional environment for data transmission, in which a wired medium such as a telephone line or network cable is relatively inexpensive to obtain and to keep open all the time.
SUMMARY OF THE INVENTION
A particular problem occurs in existing communication systems that use on-demand multiple access techniques to permit multiple users to share a physical channel. Due to the nature of Internet communications, these techniques increasingly make use of Time Division Multiplex (TDM) to assign time slots to specific users or connections on a demand basis. In such a system, time slot assignments are communicated to a receiver either explicitly or implicitly.
In an implicit assignment system, time slots are preassigned in a fixed pattern. Therefore, receivers know when to listen for data intended for them. However, implicit assignment systems are typically not flexible enough to efficiently handle Internet traffic.
In an explicit assignment system, time slots are assigned to specific users on a demand basis by a central system controller. Information as to which time slots are assigned to which connection is then explicitly communicated from the central controller to each remote unit. The overhead associated with transmitting information as to time slot assignment is therefore information bandwidth that otherwise cannot be allocated to transmitting payload data.
Unfortunately, this situation is exacerbated in a wireless communication environment in which additional radio channels must be allocated for communicating such time slot assignment information. This is a particularly acute problem on a forward link direction of such systems, that is in the direction from the network towards the user. Most Internet traffic is typically communicated in the forward direction.
The present invention seeks to overcome these difficulties. Specifically, the invention is used in a Time Division Multiplex (TDM) communication system where a physical radio communication channel, which may be defined by CDMA codes or in other ways, is shared among multiple users or connections through the use of time slots. Time slots are allocated on a demand basis. For example, a given radio channel in a forward direction is allocated only for a pre-determined time slot duration and only as needed by specific connections.
The invention overcomes certain disadvantages of prior art systems. In order to minimize overhead in the allocation of time slots to specific users, no specific time slot assignment information needs to be communicated to the receiver. However, time slot assignment may still be made on a demand basis.
This is accomplished through the use of a particular coding scheme at the transmitter, and a particular protocol at the receiver. The transmit coding scheme takes a data packet and divide it into sub-packets or frames. The frames are separately assigned to time slots at the transmitter, driven by connection demand. Each given frame is first encoded by a Forward Error Correction (FEC) code which may typically add additional bits to the frame. A user specific cover sequence, which may, for example, be a pseudonoise (PN) sequence, is added to the frame data. The FEC encoded frame is then assigned a time slot and transmitted over the shared radio channel.
At the receiver end of the connection, all receivers always attempt to receive to all frames in all time slots. As part of this receiving process, each receiver applies its specific assigned cover sequence in order to attempt to receive each frame. The candidate frame is then submitted to an inverse FEC decoding process to attempt to properly decode each frame.
A process within a first layer of the receive protocol, which may be implementation access layer, handle the candidate frame as follows. If a frame is properly decoded, as indicated by the FEC decoding process being successfully completed, the frame is passed up to the next higher layer of the receiver protocol. However, if a frame is erroneously decoded, it is simply discarded. Most importantly, the discarded frame event does not cause any error indication to be returned to a higher layer of the protocol.
The result is that only the receivers having the correct cover sequence assigned to them will properly decode frames intended for them. Any frames decoded that are not intended for that particular receiver will therefore normally be discarded.
A higher layer of the receive protocol then takes care of the problem of erroneously discarded frames intended for the receiver and/or erroneously accepted frames that were intended for other receivers. Specifically, the higher layer protocol may determine, from information contained in a frame such as a sequence number, when such frame has been erroneously discarded or erroneously accepted. Only at this higher layer, which may be a link layer of the protocol, will a receiver issue an error indication back to the transmitter, requesting re-transmission of the packet.
There are several advantages to this arrangement.
First, only cover code information, and not time slot information, needs to be made available at each receiver. Therefore, the overhead associated with dynamic assignment and deassignment of time slots to specific receivers, such as the need to transmitting information as to time slot assignment and deassignment is eliminated.
Second, the system works especially well where the system has wireless communication or other multiple access techniques, such as Code Division Multiple Access (CDMA), to define the physical channels. Eliminating the need to transmit time slot information from the transmitter to the receiver provides for much greater flexibility on demand assignment of individual channel resources. Reducing signaling overhead demand in such systems also increases the amount of information bandwith available for carrying payload data, while decreasing the amount of channel interference, thereby increasing capacity of the system as a whole.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a block diagram of a communication system in which access is granted to a shared communication medium on a time division multiplex basis, without explicit time slot assignment information being made available to the receivers.
FIGS. 2A and 2B
are more detailed diagrams of the transmitter encoding and receiver decoding.
FIG. 3
illustrates the format of a packet and the frames contained therein.
FIG. 4
is a flowchart of the operations performed by a lower layer protocol at the receiver.
FIG. 5
is a flowchart of the operations performed by a higher layer protocol at the receiver.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1
is a block diagram of a communication system
10
that makes use of Time Division Multiplexing (TDM) to allow multiple transmitters and receivers to share access to a common channel resource on a time slot basis, without the need for explicit time slot assignment information to be made available at the receiver. In the following description, the communication system
10
is described such that the shared channel resource is a wireless or radio channel. However, it should be understood that the techniques described here may be applied to allow shared access to other types of media such as telephone connections, computer network connections, cable connections, and other physical media to which access is granted on a demand driven time slot basis.
The communication system
10
includes a number of Personal Computer (PC) devices
12
-
1
,
12
-
2
, . . .
12
-h, . . .
12
-
1
, corresponding Subscriber Access Units (SAUs)
14
-
1
,
14
-
2
, . . .
14
-h, . . .
14
-
1
, and associated antennas
16
-
1
,
16
-
2
, . . .
16
-h, . . .
16
-
1
. Centrally located equipment includes a base station antenna
18
, and a base station processor (BSP)
20
. The BSP
20
provides connections to an from an Internet gateway
22
, the Internet
24
, and network file server
30
. The system
10
is a demand access, point to multi-point wireless communication system such that the PCs
12
may transmit data to and receive data from network server
30
through bi-directional wireless connections implemented over forward links
40
and reverse links
50
. It should be understood that in a point to multi-point multiple access wireless communication system
10
as shown, a given base station processor
20
typically supports communication with a number of different subscriber access units
14
in a manner which is similar to a cellular telephone communication network.
The PCs
12
may typically be laptop computers
12
-
1
, handheld units
12
-h, Internet-enabled cellular telephones or Personal Digital Assistant (PDA)-type computers. The PCs
12
are each connected to a respective SAU
14
through a suitable wired connection such as an Ethernet-type connection.
An SAU
14
permits its associated PC
12
to be connected to the network file server
30
. In the reverse link direction, that is, for data traffic traveling from the PC
12
towards the server
30
, the PC
12
provides an Internet Protocol (IP) level packet to the SAU
14
. The SAU
14
then encapsulates the wired framing (i.e., Ethernet framing) with appropriate wireless connection framing. The appropriately formatted wireless data packet then travels over one of the radio channels that comprise the reverse link
50
through the antennas
16
and
18
. At the central base station location, the BSP
20
then extracts the radio link framing, reformatting the packet in IP form and forwards it through the Internet gateway
22
. The packet is then routed through any number and/or any type of TCP/IP networks, such as the Internet
24
, to its ultimate destination, such as the network file server
30
.
Data may also be transmitted from the network file server
30
to the PCs
12
, in a forward direction. In this instance, an Internet Protocol (IP) packet originating at the file server
30
travels through the Internet
24
through the Internet gateway
22
arriving at the BSP
20
. Appropriate wireless protocol framing is then added to the IP packet. The packet then travels through the antenna
18
and
16
to the intended receiver SAU
14
. The receiving SAU
14
decodes the wireless packet formatting, and forwards the packet to the intended PC
12
which performs the IP layer processing.
A given PC
12
and the file server
30
can therefore be viewed as the end points of a duplex connection at the IP level. Once a connection is established, a user at the PC
12
may therefore transmit data to and receive data from the file server
30
.
As will be described in greater detail later, the reverse link
50
actually consists of a number of different types of logical and/or physical radio channels including an access channel
51
, multiple traffic channels
52
-
1
, . . .
52
-t, and a maintenance channel
53
. The reverse link access channel
51
is used by the SAUs
40
to send messages to the BSP
20
to request that traffic channels be granted to them. The assigned traffic channels
52
then carry payload data from the SAU
14
to the BSP
20
. It should be understood that a given IP layer connection may actually have more than one traffic channel
52
assigned to it. In addition, a maintenance channel
53
may carry information such as synchronization and power control messages to further support transmission of information over the reverse link
50
.
Similarly, the forward link
40
typically includes a paging channel
41
. The paging channel
41
is used by the BSP
20
to not only inform the SAU
14
that forward link traffic channels
52
have been allocated to it, but also to inform the SAU
14
of allocated traffic channels
52
in the reverse link direction. Traffic channels
42
-
1
. . .
42
-t on the forward link
40
are then used to carry payload information from the BSP
20
to the SAUs
14
. Additionally, maintenance channels carry synchronization and power control information on the forward link
40
from the base station processor
20
to the SAUs
14
.
Additional information as to one possible way to implement the various channels
41
,
42
,
43
,
51
,
52
, and
53
is also provided in Patent Cooperation Treaty Application No. WO99/63682 entitled “Fast Acquisition Of Traffic Channels For A Highly Variable Data Rate,” assigned to Tantivy Communications, Inc. and published Dec. 9, 1999.
The traffic channels
42
on the formal link
40
are shared in a Time Division Multiplex scheme among a number 8 the SAUs
14
. Specifically, a typical forward link traffic channel
42
is partitioned into a predetermined number of periodically repeating time slots
60
-
1
,
60
-
2
, . . .
60
-
5
for transmission of messages to the multiple SAUs
14
. It should be understood that a given SAU
14
may, at any instant in time, have multiple time slots
60
assigned to it or at other times may have no time slots at all assigned to it.
The allocation of time slots occurs on a demand basis among the various SAUs
14
in a physical area serviced by the system
10
. The time slot assignments are typically determined by the Base Station Processor (BSP)
20
which is coordinating the assignment of resources to specific connections between users of the computers
12
and servers
30
. These assignments are made based upon a number of factors, such as traffic demand, requested quality of service, and other factors.
The manner of assignment of a specific time slot
60
to a specific one of the SAUs
14
is not of importance to the present invention. Rather, the present invention is concerned with the manner in which a receiver such as a SAU
14
may correctly receive time slotted data on the forward link without having available to it. Specific information as to which time slots are assigned to other SAUs
14
.
More particularly, refer now to
FIGS. 2A and 2B
where there is shown a generalized block diagram of the encoding process at the transmit side and decoding process at the receive side according to the invention. It should be understood that in accordance with the notation of
FIGS. 2A and 2B
, a transmitter
100
may, in the case of the forward link
40
, be the Base Station Processor (BSP)
20
shown in FIG.
1
. Likewise, the receivers
130
shown in
FIGS. 2A and 2B
are one or more of the SAUs
14
shown in FIG.
1
.
At the transmitter
100
, a packet containing the data to be transmitted to a specific receiver i (D
i
) is first fed to a framer
102
. The framer
102
divides the packet into sub-packets or frames. The number of bytes in each of the frames, and the number of frames per packet, and the packet size is not of particular importance to the present invention. Any number of techniques can be used to determine the optimum frame size and number of frames per packet.
In any event, the framed data is then fed to a Forward Error Correction encoder (FEC)
104
. The FEC encoder
104
takes the framed data and adds additional bits to permit error detection at the receiver
130
. Any number of FEC encoder processes may be used such as BCH codes, block codes, turbo codes, turbo product codes and the like.
The FEC encoded frame is then fed to a cover sequence circuit
106
. The cover sequence modulator
106
applies a cover sequence, C
i
associated with the particular end-to-end connection that is to receive the data D
i
. A number of different cover sequences C are associated with each of a number of different connections that can be carried over the shared broadcast media
120
. The cover sequences C
i
may be any suitable sequence. For example, one class of such sequences are the long pseudorandom raise (PN) sequences. In such an instance, the cover sequence is applied by module-2 multiplication of the cover sequence C
i
with the data D
i
. Suitable cover sequences may also include other near-orthogonal sequences that scramble the data. The cover sequence selected should scramble the data sufficiently to cause the FEC decoder
134
to fail to decode it properly if an incorrect cover sequence is applied at the receiver.
It should be understood then that the coded signals output from a number of transmitters
110
may then be applied to a time division multiplexer
115
. Thus, output from a number of transmitters
110
-
1
. . .
110
i
. . .
110
t
may be fed as input to the TDM multiplexer
115
to assign time slots of the multiplexal signal
118
to particular ones of the transmitters
110
. The time division multiplexed signal
118
is then fed over the shared broadcast media
120
, to the receivers
130
, which in the preferred embodiment is the forward link
40
described in FIG.
1
.
A specific exemplary receiver
130
-
1
consists of a cover sequence circuit
132
, an FEC decoder
134
, and frame error detect
136
. More specifically, the cover sequence circuit
132
applies the cover sequence C
i
associated with a particular receiver
130
to the signal that it receives. For example, consider the case of the receiver
130
-i, which is the intended recipient for data sequence D
i
. In order to properly receive the data D
i
, cover sequence C
i
is fed to the respective cover sequence demodulator
132
-i. In the case of using long PN codes, the cover sequence circuit performs a modulo-2 multiplication by the cover sequence. Other types of cover sequences may require different processing. In any event, the output of the cover sequence demodulator
132
-i is thus the same signal
105
that was presented to the input of the corresponding sequence modulator
106
in the transmitter
110
-i.
The cover sequence signal
133
-i is then applied to the FEC decoder
134
-i to remove the FEC encoding applied at the transmitter
100
. The result is a digital signal or set of bits that represents the input frame which was output by the framer
103
at the transmitter
110
-i.
An error detect is then performed in block
136
to determine whether or not the received frame was received properly. In case that it was, the frame is marked as “passing” and then passed up to a higher lever packet assembler
150
. The pocket assembler
150
will be described in greater detail in
FIGS. 3-5
.
In the normal course of processing (i.e., when no bit errors are experienced in transmission), only a single receiver
130
-i which is the intended receiver will receive a pass indication from the output of the frame error detect
136
. The other frame error detectors
136
-
1
,
136
-
2
, . . .
136
-i−,
136
-i-i+1, . . . ,
136
-R detect will, in the normal course of events, receive a fail indication. This is because only the receiver
130
-i (having associated with it the cover sequence C
i
which was used to encode the data at the transmitter
110
-i) will cause proper output at the cover sequence demodulator
132
-i. The other cover sequence circuits
132
-
1
, . . .
132
-i−1,
132
-i+1, . . . ,
132
-R will scramble the received data such that the FEC decoder will request an error. Therefore, the frame error check process
136
associated with such other receivers will normally indicate that the frame detection failed.
Turning attention now to
FIG. 3
, the framing format for an exemplary data packet D
i
will be described prior to discussing the operation of the packet assembler
150
in detail. A packet
151
is divided into multiple frames
152
-
1
,
152
-
2
. . .
152
-M . . .
152
-X at the transmitter
110
. An exemplary frame
152
-
2
consists therefore of a section of payload data
166
taken from the packet
151
and additional information including at least a packet identifier field
162
, a packet length field
163
, a sequence number field
164
, a Cyclic Redundancy Check (CRC) field
16
.
A packet identifier
162
associated with each frame
152
indicates the particular packet with which the frame
152
is associated. The packet length field
163
indicates the length of the packet. The sequence number field
164
is a number indicating the particular order that the frame
152
-
2
occupies in the specific packet
151
. For example, the sequence number within the frame
152
-
2
(being the second frame F
2
in the packet
151
) would be a binary representation of the number “2.”
FIG. 4
is a flow chart of the operations performed by the packet assembler
150
at a lower level layer of a protocol at the receiver
130
. This protocol may typically be considered to be part of a link layer protocol that is responsible for assembling and properly detecting frames, as opposed to properly detecting the bits of each frame.
In a first step of this process, a given receiver
130
-i determines which cover sequence, C
i
, is associated with it. This information may be provided to the receiver
130
-i on a paging channel
141
associated with the forward link, such as when the base station processor
20
initially sets up a connection between a particular subscriber access unit
14
and the server
30
.
In other embodiments, the cover sequence C
i
can be pre-assigned to the particular receiver
130
-i, such as during a system configuration process.
In any event, once activated, the receiver
130
-i enters a state
210
in which it is continuously receiving bits of the frames. Upon receipt of a complete frame, the process previously described for receiver
130
-i is performed, including the cover sequence circuit
132
, FEC decoding
134
, and frame error detect
136
.
If, in state
212
, the frame error detect
136
indicates that a frame error has occurred, then processing proceeds to state
214
in which the frame is discarded. However, not only is the frame discarded at this point, but it should be noted that no error indication is provided to a corresponding link layer back at the originator of the frame such as at the server
30
, or to a higher layer at the receiver
130
.
Back in state
212
, if the frame was received without error, processing continues to state
216
in which the frame is passed up to a higher layer protocol at the receiver associated, for example, with the packet assembler
150
process.
FIG. 5
shows a flow chart of the steps performed by the packet assembler
150
to further complete the process according to the invention. Upon receipt of a frame, in state
240
, a state
242
is next entered in which the frames are assembled to complete a packet. In state
244
, if this is not the last frame of a packet, such as indicated by comparing the frame length information and the sequence number information in the packet, then processing returns to state
240
. The process then continues, with the packet assembler
150
continuing to receive frames.
In state
244
, which is entered upon an indication that the last frame has been received, then state
248
is entered in which it is determined whether or not a frame is missing. This determination can be made by examining the frame sequence numbers associated with each packet to determine if a frame is missing. Returning to
FIG. 3
, there may, for example, be in an assembled set of frames
152
-
1
,
152
-
2
, . . .
152
-x, with a particular frame
152
-m which is still missing at the time frame the last frame
152
-x is received. This missing frame, F
m
, can be due, for example, to errors which occur during transmission which caused it to be erroneously discarded by the frame error check process
136
.
In any event, if there is a missing frame
152
-m, then a state
250
is entered in which retransmission of the missing frame is requested. At this point, an error notification message is sent back to the appropriate higher level layer at the server
30
. This higher level layer may, for example, be a network layer, a transport layer, or other protocol layer above the link layer.
From state
248
, if there are no frames missing, but if an extra frame or out of sequence frame is received, such as again may be determined by comparing the packet identifier information
162
associated with each frame
152
, then a state
252
is entered. In state
252
, the out of order frame is discarded.
If there are no extra frames, that is, if all of the frames received do appear to be associated with a particular packet, then the packet has been properly received and it may be passed up to yet another, higher layer of the receiver protocol.
It should be understood that the steps
244
,
248
and
252
may be performed in any particular order. For example, missing frame determination may be made before the last frame is received and/or out of order frame or frame associated with an incorrect packet determination may also be made before either of the other two determinations.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
Claims
- 1. A method for communication in a time division multiplexed system wherein access to a shared physical channel is assigned on a demand basis by allocating timeslots to provide multiple connections between transmitters and receivers, each given connection of the multiple connections having a given receiver, the method comprising:at a transmitter, allocating at least one time slot to carry forward link packet data on a forward link channel; a dividing a given packet into at least one frame; encoding each of the at least one frames with a forward error correction code; further cover sequence encoding each of the at least one frames with a cover sequence unique to the given connection between the transmitter and the given receiver; at the given receiver, performing a cover sequence decoding process by combining a received signal with a cover sequence unique to the given receiver of the given connection, to provide a candidate frame, and decoding the candidate frame using a forward error correction decoding process, the cover sequence encoding operable to be decoded only by the cover sequence unique to the given receiver corresponding to the given connection.
- 2. A method as in claim 1 additionally comprising:if the forward error correction decoding process indicates a correctly received candidate frame, then forwarding the candidate frame to a packet assembler process in a higher level communication layer.
- 3. A method as in claim 1 additionally comprising:if the forward error correction decoding process indicates an erroneously received candidate frame, discarding the candidate frame without passing any error indication to a higher level communication layer.
- 4. A method as in claim 1 wherein the shared physical channel is a wireless channel.
- 5. A method as in claim 1 wherein the cover sequence is provided to the given receiver during a system configuration phase.
- 6. A method as in claim 1 wherein the cover sequence is provided to the given receiver in response to a channel allocation request.
- 7. A method as in claim 1 wherein the cover sequence is a long pseudorandom noise (PN) code.
- 8. A method as in claim 1 additionally comprising the step ofif frames are received out of order, requesting retransmission of missing frames at a higher level communication layer.
- 9. A method for communication in a time division multiplex system wherein access to a shared physical channel is assigned on a demand basis by allocating timeslots to provide multiple connections between transmitters and receivers, each given connection of the multiple connections having a given receiver, the method comprising:at a transmitter, allocating at least one time slot to carry forward link packet data on a forward link channel; dividing a given packet into at least one frame; encoding each of said at least one frame with a forward error correction code; further encoding each of said at least one frame with a cover sequence unique to the given connection between the transmitter and the given receiver; at the given receiver, performing a cover sequence decoding process by combining a received signal with a cover sequence unique to the given receiver of the given connection, to provide a candidate frame; decoding the candidate frame using a forward error correction decoding process; and if the forward error correction decoding process indicates an erroneously received candidate frame, discarding the candidate frame without passing any error indication to a higher level communication layer.
- 10. A method as in claim 9 additionally comprising:if the forward error correction decoding process indicates a correctly received candidate frame, then forwarding the candidate frame to a packet assembler process in a higher level communication layer.
- 11. A method as in claim 9 wherein the shared physical channel is a wireless channel.
- 12. A method as in claim 9 wherein the cover sequence is provided to the given receiver during a system configuration phase.
- 13. A method as in claim 9 wherein the cover sequence is provided to the given receiver in response to a channel allocation request.
- 14. A method as in claim 9 wherein the cover sequence is a long pseudorandom noise (PN) code.
- 15. A method as in claim 1 additionally comprising the step of:if frames are received out of order, requesting retransmission of missing frames at a higher level communication layer.
- 16. A system for communication in a time division multiplex system wherein access to a shared physical channel is assigned on a demand basis by allocating timeslots to provide multiple connections between transmitters and receivers, each given connection of the multiple connections having a given receiver, comprising:a transmitter, the given receiver having a given connection to the transmitter, a plurality of time slots operable to carry forward link packet data on a forward link channel, the packet adapted to be subdivided into frames; an FEC encoder operable to encode the frames with a forward error correction code, a cover sequence encode circuit at the transmitter operable to further encode the frames with a cover sequence unique to the given connection between the transmitter and the given receiver, a cover sequence decode circuit at the given receiver operable to decode a transmitted frame by combining a received signal with a cover sequence unique to the given receiver of the given connection to provide a candidate frame, an FEC decoder at the given receiver operable to decode the FEC code using a forward error correction decoding process, the cover sequence encoding operable to be decoded only by the cover sequence unique to the given receiver corresponding to the given connection.
- 17. The system as in claim 16 wherein the cover sequence decoder circuit is further operable to, in the case of an unintended frame being received, produce a decode result which will cause the FEC decoder to fail.
- 18. The system as in claim 16 wherein the FEC decoder is further operable to, if the forward error correction decoding process indicates an erroneously received candidate frame, discard the candidate frame without passing any error indication to a higher level communication layer.
- 19. The system as in claim 16 wherein the shared physical channel is a wireless channel.
- 20. The system as in claim 16 wherein the given receiver is further operable to obtain the cover sequence during a system configuration phase.
- 21. The system as in claim 16 wherein the given receiver is further operable to issue a channel allocation request in response to which a cover sequence is provided.
- 22. The system as in claim 16 wherein the cover sequence is a long pseudorandom noise (PN) code.
- 23. The system as in claim 16 wherein the given receiver is further operable to, if the frames are received out of order, request retransmission of missing frames at a higher level communication layer.
US Referenced Citations (19)