Patent Application
20080159252
1. Field of the Invention
This invention relates generally to telecommunications, and, more particularly, to wireless communications.
2. Description of the Related Art
In the field of wireless telecommunications, such as cellular telephony, a system typically includes a plurality of base stations distributed within an area to be serviced by the system. Various users within the area, fixed or mobile, may then access the system and, thus, other interconnected telecommunications systems, via one or more of the base stations. Typically, a mobile device maintains communications with the system as the mobile device passes through an area by communicating with one and then another base station, as the user moves. The mobile device may communicate with the closest base station, the base station with the strongest signal, the base station with a capacity sufficient to accept communications, etc.
Wireless telephone systems employ a variety of communications standards, including, more recently, a broadband data standard commonly known as cdma 2000 Evolution—Data Optimized (EV-DO). EV-DO has dramatically increased the system capacity. In particular, broadcast-multicast service (BCMCS) enables operators to provide a variety of high speed applications more efficiently than by using traditional unicast or point-to-point mode of communication. One example of an application that would benefit from the high speed offered by BCMCS is a group call using Voice over Internet Protocol (VoIP). Such a call may be established, for example, using popular “walkie-talkie” techniques where speech from a user controlling a communication “floor” is distributed to predefined or ad-hoc talk group members by a special server.
In a conventional EV-DO unicast mode, ACK/NACK signaling from a mobile device can terminate Hybrid ARQ retransmission early, and thus improve transmission efficiency in fading channels. In BCMCS, however, there is no such fast feedback mechanism available, because mobile devices do not need to maintain a continuous Reverse Link connection to the access network. In some applications, MAC layer Reed-Solomon codes may be used to improve performance, however, these codes introduce a substantial delay that does not meet the requirements of latency-sensitive applications such as VoIP.
In one aspect of the instant invention, a method is provided for controlling a communications system. The method comprises targeting a transmission from a base station into a first sector of a cell during a first selected portion of a communications period; targeting a transmission from the base station into a second sector of the cell during a second selected portion of a communications period; and targeting a transmission from the base station into a third sector of the cell during a third selected portion of a communications period.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Turning now to the drawings, and specifically referring to
Thus, those skilled in the art will appreciate that the communications system 100 enables the mobile devices 120 to communicate with the data network 125 and/or the PSTN 160. It should be understood, however, that the configuration of the communications system 100 of
As is illustrated in
Referring now to
The mobile device 120 shares certain functional attributes with the base station 130. For example, the mobile device 120 includes a controller 250, an antenna 255 and a plurality of channels: such as a shared channel 260, a data channel 270, and a control channel 280. The controller 250 generally operates to control both the transmission and reception of data and control signals over the antenna 255 and the plurality of channels 260, 270, 280.
Normally, the channels 260, 270, 280 in the mobile device 120 communicate with the corresponding channels 220, 230, 240 in the base station 130. Under the operation of the controllers 210, 250, the channels 220, 260; 230, 270; 240, 280 are used to effect a controlled scheduling of communications from the mobile device 120 to the base station 130.
Turning now to
In one embodiment of the instant invention, communications from neighboring base stations 130 are coordinated so that they occupy different time slots to transmit broadcast-multicast contents to avoid collisions or interference. The coordination may not need to be dynamic and certain time slot planning can be pre-configured before the system is started. Also, the synchronization requirement for such coordination is rather loose: the timing offset between neighboring base stations/sectors (including the propagation delay difference at the mobile) can be in a range of about 40 to 50 μs.
One example of a slot-reuse mechanism for EV-DO BCMCS that may be used to reduce interference between neighboring base stations 130 is shown in
A more detailed structure of a time slot is shown in a magnified region 400 in
In one embodiment of the instant invention, the three base station/sector slot-reuse is applied to a four-interlace structure employed in an EV-DO forward link, by assigning Sector 1, Sector 2, and Sector 3 to occupy the first, second and third interlace, respectively. The fourth interlace of the EV-DO forward link is transmitted in Sector 1 during the first 12 time slots, in Sector 2 during the next 12 time slots, and in Sector 3 during the further next 12 time slots, and so on, as
In the illustrated embodiment, each sector of the base station 130 can use only one-third of the slot resource. Thus, on a per-sector basis, the data rate is one-third of the rates listed in
SNR at cell edges is significantly improved so that the systems can support high data rate with good coverage, especially for broadcast-multicast service where the forward link coverage is a significant performance metric by service providers. With the slot-reuse pattern described in
To further improve efficiency, it may be useful to employ a dynamic slot-reuse allocation rather than the fixed method described above. In situations where dynamic slot-reuse is implemented, those skilled in the art will appreciate that coordination between the base stations 130 may be used to avoid slot-usage collisions. Such coordination may be accomplished by communications directly between the various base stations or through intermediary devices, such as the RNC.
Those skilled in the art will appreciate that the various system layers, routines, or modules illustrated in the various embodiments herein may be executable control units (such as the controllers 210, 250 (see
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Consequently, the method, system and portions thereof and of the described method and system may be implemented in different locations, such as the wireless unit, the base station, a base station controller and/or mobile switching center. Moreover, processing circuitry required to implement and use the described system may be implemented in application specific integrated circuits, software-driven processing circuitry, firmware, programmable logic devices, hardware, discrete components or arrangements of the above components as would be understood by one of ordinary skill in the art with the benefit of this disclosure. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
