Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-10-27
2004-12-07
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S348000, C370S462000, C455S452200
Reexamination Certificate
active
06829227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to packet data communication systems and, more specifically, to an apparatus, method and system for a dual polling media access control protocol for packet data in fixed wireless local loop CDMA-based communication systems.
BACKGROUND OF THE INVENTION
Fixed wireless communication systems are becoming increasingly viable solutions for providing local loop telecommunication network access, particularly in developing nations. The alternative, wireline local loop access, may be prohibitively expensive, with a sparse availability of wireline telecommunication systems operating as a constraint on economic development. As a consequence, telecommunication service providers are increasingly turning to wireless technologies, with or without wireline services, to implement a cost-effective local loop telecommunication service, for voice, data, and other multimedia uses.
A wireless local loop (“WLL”) system typically includes a base station which transmits to and receives from various transceivers (within subscriber units) which are located at each home, business or other customer premises being served. The base station broadcasts to all the subscriber units it serves (“forward”, “downlink” or “downstream” direction). The broadcast includes an identification of the intended subscriber unit, which then selects that broadcasted information for the particular customer premises. Similarly, when it has information to send, each subscriber unit transmits the information to the base station (“reverse”, “uplink” or “upstream” direction). These upstream transmissions are typically separated by time (time division multiple access (TDMA)), frequency (frequency division multiple access (FDMA)), or code (code division multiple access (CDMA)), creating multiple channels which, to some degree, prevent the subscriber units from contending for the same resources. As all subscriber units are not anticipated to be constantly transmitting, for cost-effectiveness and other efficiency considerations, system providers may allocate system resources so that upstream channels are shared among multiple subscriber units, creating an inherent potential for conflict on each such shared upstream channel.
As a consequence, for packet data systems with a number of subscribers sharing the same radio or channel resources, a protocol is needed to resolve the potential contention among subscriber units for the available upstream channels. Existing CDMA-based packet radio systems utilize a random access media access control (“MAC”) protocol, in which a transmission of a single data packet in a given time period is generally received correctly, while simultaneous transmission of an additional packet causes a collision, with all packets destroyed.
One such random access protocol is ALOHA (see, e.g., A. Tanenbaum,
Computer Networks
(3d. ed. 1996) at 246-50). When data arrives at the subscriber unit for upstream transmission, such as from a computer within the customer premises, it is transmitted immediately. When the base station receives an uncorrupted packet, the base station broadcasts an acknowledgement to the sender. If no acknowledgement is received, the transceiver “backs off” for a random period of time, and then retransmits the packet. If two or more transmissions overlap in time (collide), all are corrupted, and the base station does not acknowledge any of them. Another variant of ALOHA, slotted ALOHA, provides for upstream transmissions in unassigned time slots, but still has a significant probability of collisions within these time slots.
Most random access protocols, such as ALOHA and its variants, are inherently unstable, and statistical fluctuations may easily cause their saturation. These protocols tend to reach a situation in which the percentage of sources attempting to retransmit approaches one hundred percent, while the throughput approaches zero. In addition, with this inherent instability, a system with a random access protocol must be periodically reset to operate in its stable region of its throughput-channel traffic rate curve. As a consequence, while delay and throughput characteristics may be satisfactory in the short term, they are quite poor over a long period of time.
Additionally, protocols such as ALOHA require a very low loading to work with any efficiency. They require a small packet size, or the probability of collision becomes excessively high, and have a low maximum throughput (e.g., approximately 18%). In addition, there is no theoretical bound for transmission delay, especially for users with comparatively infrequent or small data transmissions.
Other protocols, which may be suitable for wireline or cable applications, are unsuitable for fixed wireless applications. For example, in Carrier Sense Multiple, Access (CSMA) and Digital Sense Multiple Access (DSMA), when a user has data to transmit, the transceiver looks for current activity on the selected channel, and if there is no activity, it transmits. For radio applications, this would rely upon time division duplexing, as corresponding transceivers (within subscriber units) would have to both transmit and receive on the same frequency. For fixed wireless applications, there is an additional difficulty because the transceivers are directional and cannot directly receive transmissions from other transceivers, making direct carrier sense impossible.
In DSMA, activity on the uplink (upstream) channel is broadcast by the a base station to the subscriber units on the downlink channel(s). As a consequence, the effectiveness of DSMA in preventing data collisions depends upon the accuracy of the sensing operation by the transceivers. In addition, there is a period of vulnerability, corresponding to the time required for the broadcast to be received by all subscriber units. During this period, other users may still perceive the channel as idle, start a transmission, and cause a collision.
Another difficulty for any desired protocol arises within CDMA-based communication systems, namely, power control. More specifically, any packet data protocol for use with CDMA requires power control over the various transceivers, to have the same received power at the base station, to avoid increased noise levels and interference with other transceivers. In circuit switched systems, such as CDMA-based voice telephony, upstream transmission is effectively continuous, for the entire duration of the communication session, allowing correspondingly continuous power measurement and power correction. In contrast, packet data transmission is generally bursty, with transceivers transmitting for a short duration, followed by no transmission, followed by another transmission burst, and so on. A mechanism is needed in a wireless protocol for dynamic power control, to account for highly variable transmission characteristics and to accommodate bursty traffic patterns.
As a consequence, a need remains for a deterministic protocol for upstream or uplink packet data transmission in a wireless local loop communication system. Such a protocol should have guaranteed maximum delay and minimum throughput characteristics. Such a protocol should provide for maximal throughput, with minimum delay, for delay-sensitive data packets. The various embodiments of the deterministic protocol should also provide power control, for fixed wireless transmission systems, during data transmission.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus, method and system are provided for a dual polling media access control (“MAC”) protocol, which has guaranteed maximum delay and minimum throughput characteristics. The various embodiments of the deterministic protocol of the present invention also provide for power control, for fixed wireless transmission systems, both during data transmission and in between data transmissions. As a consequence, when data is transmitted, the initial power setting is approximately correct.
The preferred system embodiment includes a plurality of subscriber units, a base station h
Pitt Randall Evans
Spears David Warren
Trabelsi Chokri
Kizou Hassan
Lucent Technologies - Inc.
Sefcheck Gregory
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