BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The invention will be more fully understood with reference to the following Detailed Description of the Invention in conjunction with the drawings of which:
FIG. 1 is a block diagram of a conventional wireless communications system for transmitting multiple data streams over a point-to-point radio link;
FIG. 2
a depicts two high priority data streams transmitted by the conventional system of FIG. 1, in which the high priority data is multiplexed onto a radio link with excess capacity;
FIG. 2
b depicts two high priority data streams and a single low priority data stream transmitted by the conventional system of FIG. 1, in which the high priority data is multiplexed onto a radio link with the low priority data;
FIG. 3 is a block diagram of a wireless broadband communications system for transmitting multiple streams of high and lower priority data over a TDD point-to-point radio link according to the present invention;
FIG. 4 depicts two high priority data streams and a single low priority data stream transmitted by the system of FIG. 3, in which low priority frames are fragmented to form a plurality of fragmented packets to reduce the latency for the high priority data;
FIG. 5 depicts an illustrative structure of the fragmented packets of FIG. 4; and
FIG. 6 is a flow diagram of a method of operating the system of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
A wireless broadband communications system and method is disclosed that achieves reduced latency for delay-critical, high priority data when such data is multiplexed with lower priority data for transmission over a time division duplex (TDD), adaptively modulated, point-to-point radio link. The presently disclosed wireless communications system can be employed to multiplex high and lower priority data streams for transmission over the same radio link, while maintaining the latency for the high priority data at an acceptable level.
FIG. 1 depicts a conventional wireless communications system 100 configured to transmit multiple data streams over a TDD point-to-point radio link 112. As shown in FIG. 1, the conventional system 100 includes two radio stations 102.1-102.2 and two antennas 110.1-110.2. The radio station 102.1 is coupled to two high priority E1/T1 communications links 104.1, 106.1, and a single low priority Ethernet communications link 108.1. Similarly, the radio station 102.2 is coupled to two high priority E1/T1 communications links 104.2, 106.2, and a single low priority Ethernet communications link 108.2. For example, each of the links 104.1, 106.1, 108.1 may be implemented by a copper or optical fiber cable. The E1/T1 link 104.1 provides a first high priority data stream including a plurality of packets A to the radio station 102.1, and the E1/T1 link 106.1 provides a second high priority data stream including a plurality of packets B to the radio station 102.1. Further, the Ethernet link 108.1 provides a low priority data stream including at least one frame C to the radio station 102.1. The radio station 102.1 is configured to transmit the high and low priority data streams over the radio link 112 via the antenna 110.1, and the radio station 102.2 is configured to receive the transmitted data via the antenna 110.2. It is noted that the rate of data transmission over the radio link 112 can vary with atmospheric conditions, which can adversely affect the propagation of wireless signals over the link. Finally, the radio station 102.2 provides the high priority packets A, B on the E1/T1 links 104.2, 106.2, respectively, and provides the low priority frame on the Ethernet link 108.2.
FIG. 2
a illustrates two high priority E1/T1 data streams that may be provided via the respective E1/T1 links 104.1, 106.1 for transmission by the radio station 102.1 (see FIG. 1). As shown in FIG. 2a, a first high priority E1/T1 data stream is segmented into a plurality of packets A1-A5, and a second high priority E1/T1 data stream is segmented into a plurality of packets B1-B5. In this illustrative example, it is assumed that each of the high priority data streams is continuous, and that the size of each of the packets A1-A5, B1-B5 is adjusted to match or be a fraction of the capacity of a TDD burst, thereby making the process of assembling the TDD bursts more efficient. The pluralities of packets A1-A5, B1-B5 corresponding to the two respective E1/T1 data streams are multiplexed onto a shared transmission medium such as the radio link 112 (see FIG. 1), which, in this example, has a data capacity that exceeds the combined data capacity of the two E1/T1 links 104.1, 106.1. For example, the multiplexed packets A1-A5, B1-B5 may be arranged in a sequence in an alternating fashion, e.g., A5, B5, A4, B4, A3, B3, A2, B2, A1, B1, as depicted in FIG. 2a. In this way, the pluralities of packets A1-A5, B1-B5 can be efficiently multiplexed together so that one data stream does not significantly impede the other data stream, thereby avoiding excessive latency for the data. For example, dummy data packets may be stuffed into the data stream between adjacent packets A and B to fill the excess capacity of the radio link 112.
FIG. 2
b illustrates the two high priority E1/T1 data streams provided via the respective E1/T1 links 104.1, 106.1, and a single low priority Ethernet data stream provided via the Ethernet link 108.1, for transmission by the radio station 102.1 (see FIG. 1). As shown in FIG. 2b, one of the high priority E1/T1 data streams is segmented into the plurality of packets A1-A5, and the other high priority E1/T1 data stream is segmented into the plurality of packets B1-B5. As in the first example of FIG. 2a, it is assumed that each of the high priority data streams is continuous, and that the size of each of the packets A1-A5, B1-B5 is adjusted to match or be a fraction of the capacity of a TDD burst. The low priority Ethernet data stream includes at least one frame C. The pluralities of packets A1-A5, B1-B5 and the frame C are multiplexed onto a shared transmission medium such as the radio link 112 (see FIG. 1). Whereas, in the example of FIG. 2a, the pluralities of packets A1-A5, B1-B5 can be efficiently multiplexed together so that one data stream does not significantly impede the other data stream, the addition of the low priority Ethernet frame C to the multiplexed high priority E1/T1 packets A1-A5, B1-B5 introduces a significant delay in the transmission of the high priority data. For example, as shown in FIG. 2b, if the packets A1-A5, B1-B5 and the frame C are arranged in a sequence for transmission over the radio link 112 such that the frame C is disposed between the packets A4 and B5, then a significant delay is introduced between the packets A4 and B5 in the sequence, thereby causing increased latency for the high priority E1/T1 data streams.
FIG. 3 depicts an illustrative embodiment of a wireless broadband communications system 300 for transmitting multiple streams of high and low priority data over a TDD point-to-point radio link 312, in accordance with the present invention. The wireless broadband communications system 300 may be employed to transmit multiple data streams having different levels of priority over the same radio link, while maintaining the latency for high priority data at an acceptable level. In the illustrated embodiment, the wireless communications system 300 includes two radio stations 302.1-302.2. The radio station 302.1 includes a plurality of queues Q1-Q4 for buffering the multiple data streams based upon their corresponding priority levels. For example, the plurality of queues may include two high priority queues Q1 and Q2, a mid-level priority queue Q3, and a low priority queue Q4. As shown in FIG. 3, the two high priority queues Q1, Q2 are coupled to two high priority E1/T1 communications links 304.1, 306.1, respectively. The E1/T1 link 304.1 provides a first high priority data stream including a plurality of packets A to the high priority queue Q1, and the E1/T1 link 306.1 provides a second high priority data stream including a plurality of packets B to the high priority queue Q2. Because the data structure of an Ethernet data stream may include frames or packets having respective headers that define the type of data service being provided (e.g., mid-level or low priority data), the radio station 302.1 includes a data prioritizor 314 coupled to a low priority Ethernet communications link 308.1. The Ethernet link 308.1 provides mid-level and/or low priority Ethernet frames to the data prioritizor 314, which is configured to determine the type of data service being provided by examining the frame headers, and to buffer the frames in the mid-level and low priority queues Q3, Q4 based upon their respective levels of priority.
The radio station 302.1 also includes two frame fragmentors 318a-318b coupled to the mid-level priority queue Q3 and the low priority queue Q4, respectively; an adaptive modulation and fragmentation controller 322; a data multiplexor 320; and a radio transmitter 310.1 including an antenna (not shown). The adaptive modulation/fragmentation controller 322 enables the frame fragmentors 318a-318b to fragment the frames contained in the mid-level and low priority queues Q3, Q4 based at least in part upon the current data capacity of the radio link 312, which may depend on whether the conditions for wireless signal propagation on the link 312 are favorable or unfavorable.
For example, when propagation conditions are favorable, the frame fragmentors 318a-318b may not operate to fragment the frames contained in the lower priority queues Q3 and Q4, but may instead provide these frames to the data multiplexor 320 in their un-fragmented form. However, when propagation conditions are less favorable due to, e.g., reduced bandwidth availability and/or adverse atmospheric conditions, the adaptive modulation/fragmentation controller 322 may direct the radio transmitter 310.1 to select a modulation format that is less spectrally efficient, reducing the data capacity of the radio link 312. Because the data capacity of the radio link 312 is reduced, the adaptive modulation/fragmentation controller 322 may then direct the frame fragmentors 318a-318b to fragment the frames contained in the mid-level and low priority queues Q3 and Q4, respectively, to form pluralities of fragmented packets of reduced size. The size of the fragmented packets depends on the data rate that can be achieved on the radio link 312, which in turn is dependent on the state of the adaptive modulation/fragmentation controller 322. Because frame fragmentation is generally a bandwidth inefficient process, the frame fragmentors 318a-318b fragment the frames contained in the lower priority queues Q3 and Q4 only when necessary to maintain the latency for the data within acceptable limits. The data multiplexor 320 receives the E1/T1 packets A and B from the high priority queues Q1 and Q2, respectively, and the un-fragmented or fragmented Ethernet frames from the frame fragmentors 318a-318b. The data multiplexor 320 then multiplexes the high priority E1/T1 packets A and B with the mid-level and low priority Ethernet frames for subsequent transmission by the radio transmitter 310.1 over the radio link 312 as wireless signals.
The radio station 302.2 includes a radio receiver 310.2 including an antenna (not shown), a data de-multiplexor 324, and two frame re-assemblers 326a-326b. The radio receiver 310.2 is configured to capture the wireless signals including the multiplexed high priority packets and mid-level and low priority frames transmitted over the radio link 312, and to employ suitable signal processing techniques for decoding and demodulating the signals to recover the user data. The decoded and demodulated data are provided to the de-multiplexor 324, which de-multiplexes the data to recover the high and lower priority data, provides the high priority data stream including the packets A to an E1/T1 communications link 304.2, and provides the high priority data stream including the packets B to an E1/T1 communications link 306.2. The de-multiplexor 324 also provides the mid-level and low priority Ethernet frames to the frame re-assemblers 326a-326b, respectively. If the propagation conditions on the radio link 312 were such that fragmentation of the Ethernet frames by the frame fragmentors 318a-318b was deemed appropriate, then the frame re-assemblers 326a-326b operate to reassemble the fragmented mid-level and low priority frames, and to provide the re-assembled frames to Ethernet communications links 309a-309b, respectively.
It is noted that in a typical TDD system, both a transmitter and a receiver are provided at each end of a radio link, thereby allowing the system to transmit and receive data signals alternately at each end of the link. FIG. 3 depicts the radio station 302.1 transmitting data streams at one end of the radio link 312, and the radio station 302.2 receiving the data streams at the other end of the link 312, for clarity of illustration. It is further noted that the radio link 312 may comprise a point-to-point or point-to-multipoint radio link. Moreover, each of the E1/T1 links 304.1, 306.1 and the Ethernet link 308.1 may operate independently, and may carry data traffic having different levels of priority and different levels of acceptable latency for the data. In addition, each of the links 304.1, 306.1, 308.1 may carry one or more data streams, each of which may have a different priority level and different latency requirements. The multiple data streams carried by the links 304.1, 306.1, 308.1 are multiplexed together by the data multiplexor 320, using any suitable time division multiplexing technique, so that the latency requirements for the data are not violated, regardless of the data rate that can be achieved on the radio link 312 at a given time. To that end, each data stream carried by the links 304.1, 306.1, 308.1 is buffered separately in one of the queues Q1-Q4 based upon the level of priority of the data. Further, each of the data streams buffered in the queues Q1-Q4 may be segmented to form a plurality of frames or packets. The frames in the lower priority queues Q3-Q4 may then be fragmented by the frame fragmentors 318a-318b, depending on the current data capacity of the radio link, to form a plurality of fragmented packets of reduced size. Finally, the high priority packets and the un-fragmented or fragmented lower priority packets are time division multiplexed by the data multiplexor 320 for subsequent transmission in a sequence by the radio transmitter 310.1 over the radio link 312, while maintaining the latency for the high priority data at an acceptable level.
The operation of the presently disclosed wireless broadband communications system 300 will be better understood with reference to the following illustrative example and FIGS. 3-5. FIG. 4 illustrates two high priority E1/T1 data streams provided via the respective E1/T1 links 304.1, 306.1, and a single low priority Ethernet data stream provided via the Ethernet link 308.1, for transmission by the radio station 302.1 (see FIG. 3). As shown in FIG. 4, one of the high priority E1/T1 data streams is segmented into a plurality of packets A1-A5, and the other high priority E1/T1 data stream is segmented into a plurality of packets B1-B5. Further, the low priority Ethernet data stream includes at least one frame C. In this example, it is assumed that each of the high priority data streams is continuous. In addition, it is assumed that the bandwidth availability and/or the atmospheric conditions are such that the adaptive modulation/fragmentation controller 322 directs the radio transmitter 310.1 to select a modulation format that is less spectrally efficient, reducing the data capacity of the radio link 312.
Because the data capacity of the radio link 312 is reduced due to reduced bandwidth availability and/or adverse atmospheric conditions, the adaptive modulation/fragmentation controller 322 directs the frame fragmentors 318a-318b to fragment the Ethernet frame C to form a plurality of fragmented packets C1-C4 of reduced size. The data multiplexor 320 multiplexes the pluralities of high priority data packets A1-A5, B1-B5 and the low priority fragmented data packets C1-C4 by arranging the packets in a sequence, e.g., A5, B5, C4, A4, C3, B4, C2, A3, C1, B3, A2, B2, A1, B1, as depicted in FIG. 4, or any other suitable packet sequence. In this example, the size of the fragmented packets C1-C4 corresponds to the size of timeslots occurring between the high priority packets A1-A5, B1-B5. Specifically, the size of the fragmented packets C1, C2, C3, and C4 corresponds to the size of the timeslots between the packets A3 and B3, B4 and A3, A4 and B4, and B5 and A4, respectively, in the packet sequence.
In addition, because the packet sequence is to be transmitted over a TDD point-to-point radio link, the size of the fragmented packets C1-C4 is adjusted to match or be a fraction of the capacity of the TDD transmission bursts, thereby making the process of assembling the TDD bursts more efficient. It is noted that the capacity of the TDD transmission bursts is dependent on the state of the adaptive modulation/fragmentation controller 322. For example, by adjusting the size of the fragmented packets C1-C4 to match the capacity of the TDD transmission bursts, alternate TDD bursts can be made to carry alternate data streams. Further, by adjusting the size of the fragmented packets C1-C4 to be a fraction of the capacity of the TDD transmission bursts, each TDD burst can be made to carry packets from a plurality of data streams.
The radio transmitter 310.1 transmits the packet sequence over the radio link 312 as a wireless signal under control of the adaptive modulation/fragmentation controller 322. The radio receiver 310.2 receives the transmitted signal, demodulates and decodes the received signal as appropriate, and provides the demodulated and decoded signal to the data de-multiplexor 324, which de-multiplexes the packet sequence to recover the two high priority E1/T1 data streams including the pluralities of packets A1-A5, B1-B5, and the fragmented packets C1-C4. In addition, the frame re-assemblers 326a-326b reassemble the low priority Ethernet data stream from the fragmented packets C1-C4 to recover the original data format of the Ethernet frame C. Although multiplexing the two high priority data streams with the fragmented, low priority packets C1-C4 for transmission over the radio link 312 may introduce a delay in the transmission of the low priority Ethernet frame C, reduced levels of delay or latency are introduced for the delay-critical, high priority data represented by the packets A1-A5, B1-B5.
FIG. 5 depicts illustrative data structures of the Ethernet frame C, the fragmented packets C1-C4 corresponding to the frame C, and a TDD transmission burst including portions of the high priority packets A1-A5, B1-B5 and the fragmented, low priority packets C1-C4. As shown in FIG. 5, the Ethernet frame C includes a frame header 502. It is noted that the Ethernet frame C may have a length of up to 1500 bytes plus the header 502 for typical Ethernet applications, up to about 9000 bytes for proprietary “jumbo” packets, or any other suitable length. If the propagation conditions on the radio link are such that fragmentation of the Ethernet frame C is deemed appropriate, then the frame C may be divided into four fragments, or any other suitable number of fragments, as represented by the fragmented packets C1-C4. Each of the fragmented packets C1, C2, C3, C4 includes a fragmentation header 504.1, 504.2, 504.3, 504.4, respectively, which identifies the fragmented packet C1-C4 associated therewith. In the illustrative data structure of FIG. 5, the fragmented packet C4 also includes the frame header 502. The fragmentation headers 504.1-504.4 are removed when the Ethernet frame C is re-assembled at the receiver. The fragmented packets C1-C4 may be transmitted over the radio link in one or more TDD bursts with other packets from other data streams. As shown in FIG. 5, one of the TDD bursts may include the packets B4, A4, B5, A5 from the high priority E1/T1 data streams, and the fragmented packet C4 from the lower priority Ethernet frame C, arranged in a sequence, e.g., B4, A4, C4, B5, A5, or any other suitable sequence. Each of the packets B4, A4, C4, B5, A5 in the packet sequence includes a radio header 506.1, 506.2, 506.3, 506.4, 506.5, respectively, which identifies the packet associated therewith. The radio headers 506.1-506.5 are removed when the high priority data streams and the lower priority Ethernet frame are recovered at the receiver.
A method of operating the wireless broadband communications system 300 is described below with reference to FIGS. 3 and 6. The wireless communications system 300 employs time division multiplexing to transmit a plurality of data streams of different priorities over the same radio link, while reducing latency associated with at least one high priority data stream transmitted over the link. As depicted in step 602, the high priority data stream is segmented to form a plurality of packets of high priority. It is noted that the plurality of data streams includes at least one lower priority data stream, which includes at least one packet of lower priority. Further, each of the high priority and lower priority packets has a corresponding length. Next, the high priority packets are arranged in a sequence, as depicted in step 604. The positions of the high priority packets in the sequence are defined by a plurality of timeslots. Moreover, each of the high priority packets in the sequence occupies a respective timeslot. In addition, at least some of the high priority packets in the sequence are separated by at least one unoccupied timeslot. The lower priority packet is then fragmented to form a plurality of fragmented packets of lower priority, as depicted in step 606. Each of the plurality of fragmented packets has a reduced length. Next, the fragmented packets of lower priority are inserted into unoccupied timeslots separating at least some of the high priority packets in the sequence, so that at least one fragmented packet occupies a respective one of the timeslots separating the high priority packets, as depicted in step 608. Finally, the sequence of high priority packets and fragmented packets of lower priority is transmitted over the radio link as at least one wireless signal, as depicted in step 610.
It should be appreciated that the functions necessary to implement the present invention may be embodied in whole or in part using hardware, software, firmware, or some combination thereof using micro-controllers, microprocessors, digital signal processors, programmable logic arrays, or any other suitable types of hardware, software, and/or firmware.
It will further be appreciated by those of ordinary skill in the art that modifications to and variations of the above-described system and method of reducing latency by adaptive packet fragmentation may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.
Patent Application
20080056192
