In wireless communications networks, deploying relay stations close to the cell edges can improve the network performance in terms of throughput and reliability, since the signal strength and/or signal quality may otherwise be marginal in those areas. However, the operator of the network has to pay for the real estate cost of each of the relay locations, and that cumulative cost can be considerable. Another issue in conventional wireless networks is that the base stations typically use a hard-wired ‘backbone’ network to communicate with each other. Although this backbone allows a base station to exchange information with base stations that are far away (e.g., in another state), using a network this large and complex frequently introduces a large amount of latency into such communications. This latency may introduce unacceptable delays into communications between base stations in adjacent cells that need to coordinate time-critical activities with each other.
Some embodiments of the invention may be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:
In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
References to “one embodiment”, “an embodiment”, “example embodiment”, “various embodiments”, etc., indicate that the embodiment(s) of the invention so described may include particular features, structures, or characteristics, but not every embodiment necessarily includes the particular features, structures, or characteristics. Further, some embodiments may have some, all, or none of the features described for other embodiments.
In the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” is used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” is used to indicate that two or more elements co-operate or interact with each other, but they may or may not be in direct physical or electrical contact.
As used in the claims, unless otherwise specified the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common element, merely indicate that different instances of like elements are being referred to, and are not intended to imply that the elements so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
Various embodiments of the invention may be implemented in one or any combination of hardware, firmware, and software. The invention may also be implemented as instructions contained in or on a computer-readable medium, which may be read and executed by one or more processors to enable performance of the operations described herein. A computer-readable medium may include any mechanism for storing, transmitting, and/or receiving information in a form readable by one or more computers. For example, a computer-readable medium may include a tangible storage medium, such as but not limited to read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; a flash memory device, etc. A computer-readable medium may also include a propagated signal which has been modulated to encode the instructions, such as but not limited to electromagnetic, optical, or acoustical carrier wave signals.
The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that communicate data by using modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The term “mobile” wireless device is used to describe a wireless device that may be in motion while it is communicating.
In various embodiments of the invention in which relay stations are used with base stations in a collection of wireless network cells, some of the relays from different cells may be co-located and communicate directly with each other to pass information from one base station to another without having to depend on the conventional backbone network for such inter-base station communication and co-ordination. In some embodiments, the co-located relays may exchange information in the digital domain through a wired connection. In other embodiments, the co-located relays may exchange information through a fast wireless link (such as but not limited to a wireless local area network). In still other embodiments, a single relay station may wirelessly communicate directly with two or more base stations to transmit information between those base stations. Not only will this approach save real estate costs by reducing the number of locations needed for the relay stations, but it may be potentially faster than a wired backbone because the relays do not have to share a wired network with many other stations for this communication.
Within the context of this document, a “base station” is a wireless communications device that provides overall centralized scheduling for communications by other wireless devices that are associated with that base station. Base stations may also be labeled with other terms, such as network controller, access point, etc., and the term “base station” in this document is meant to encompass such devices that are labeled with other terms, unless the accompanying description explicitly excludes them. Within the context of this document, the term “associated” refers to a base station and another wireless communications device establishing an agreed-upon communications relationship with each other, such that they may communicate with each other following specific rules of format, protocol, timing, and frequency(s). In this document, the term “associated” is used to refer to a subscriber station that communicates directly with the base station, or indirectly with the base station through a relay station, and may also be used to refer to the relay station that communicates directly with the base station. In most such associations, the base station generally controls when the other devices may communicate with it (and communicate with each other, when applicable), but there may also be instances in which the other device is able to communicate without such direct control by the base station.
In this example relay station RS1 communicates with base station BS1 to relay communications between BS1 and the SS's that are associated with BS1. Similarly, RS2 communicates with BS2, and RS3 communicates with BS3, to relay information to their respective SS's. Only relay stations RS1, RS2, and RS3 are labeled, but the principles described here may be applied to some or all of the other relay stations indicated as circles in the drawing in other cells. In actual operation, the physical placement of the RS's and the shape of the cells will usually not be as orderly as shown in the drawings (e.g., the drawing shows symmetrically-formed hexagonal cells, relay stations at regular points in each cell, etc.), but the general principles described here may be applied in full or in part to many actual physical layouts.
Sometimes, two nearby BS's may need to exchange time-critical information with each other. Such information may include things such as, but not limited to: 1) the imminent handover of an SS from one BS to another, 2) allocation of non-interfering frequencies along the shared cell edge of adjacent cells (fractional frequency reuse), 3) directional interference nulling in the region of the shared cell edge of adjacent cells, 4) allocation of non-interfering time slots in the region of the shared cell edge of adjacent cells, 5) uplink sounding, 6) etc. Exchanging this information through the conventional wired backbone that connects many base stations to each other may introduce communication latencies that are too large to reliably handle this time-critical information.
Communications link L12 may take any of various forms, such as but not limited to: 1) a hardwired communication link such as a data cable, 2) a short range high-speed wireless link (e.g., Bluetooth, piconet, etc.), 3) a storage unit, such as shared RAM memory, that is accessible by both RS1 and RS2, 4) etc. RS1 and RS2 may also be co-located. This co-location may be implemented in various ways, such as but not limited to: 1) processing units for the relay stations may be located in the same structure (e.g., building, cabinet, etc.), 2) antennas for the relay stations may be mounted on the same tower, 3) the relay stations may be located close together without any common physical structure, 4) etc. Although only two relay stations are shown in
At 320, BS1 may transmit the message to RS1, with sufficient information that RS1 is aware that this message is to be communicated to RS2 rather than to one of the subscriber stations associated with BS1. At 325 RS1 may receive the message from BS1, and at 330 RS1 may then communicate the message to RS2 for eventual delivery to BS2. As previously described, the communication between RS1 and RS2 may take any of various forms. In some embodiments, the communication between RS1 and RS2 may be at the digital level, for example through a direct-link cable, a shared storage unit, etc. In other embodiments, the communication between RS1 and RS2 may be via a modulated signal, with the relevant modulation techniques, channel access protocols, addressing, etc. In some embodiments, the communication between RS1 and RS2 may be wireless, while in other embodiments it may be through a wired connection. When RS2 obtains the message at 340, it may then transmit the message wirelessly to BS2 at 350. When BS2 receives the message from RS2 at 360, it may use the information in the message appropriately at 370.
The information in the message may be used for any feasible purpose, but one of the more common purposes may be to coordinate various communication activities by BS1 and BS2, coordination that is sufficiently time-critical that communicating the information through the normal backbone network could introduce unacceptable delays. Such activities may include things such as, but not limited to: 1) a possible or definite handoff of a subscriber station between BS1 and BS2, 2) beamforming activities by various devices in the two networks so that a device in one network is unlikely to interfere with a device in the other network, 3) frequency assignments among devices in the two networks near the shared cell edge boundaries so that a device in one network is unlikely to interfere with a device in the other network, 4) etc.
Although the foregoing descriptions only describe two co-located relay stations, to exchange information between two base stations, the principles described may easily be extended to cover three or more co-located relay stations to forward information between three or more base stations. In some embodiments, the relay stations may be fixed in place (e.g., located in a building, fixed to a structure, etc.), while in other embodiments the relay stations may be mobile (e.g., in/on a vehicle, hand-carried, etc.).
Similar functionality may be provided for antenna 421 by demodulator 426, ADC 425, DAC 427, modulator 428, and amplifier 429.
The previous descriptions have focused on communications from a first base station, communications that are intended by that first base station to be routed through the relay station to a second base station (e.g., by having the second base station's address listed as the ultimate destination). But in other embodiments, the relay station itself may decide to route a communication to the second base station, even though the second base station was not listed as the ultimate destination by the first base station. For example, when BS1 schedules communications in its network by distributing a downlink MAP to the devices in BS1's network (including a relay station RS), the RS may determine that the MAP would be beneficial to BS2 in an adjacent network. By having this MAP, BS2 can schedule communications in its own network in a way that will not interfere with communications in BS1's network. In this instance, RS may forward the MAP to BS2, either directly (if RS is associated with both base stations as in
The foregoing description is intended to be illustrative and not limiting. Variations will occur to those of skill in the art. Those variations are intended to be included in the various embodiments of the invention, which are limited only by the scope of the following claims.