Patent Application
20080004016
The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding items throughout and wherein:
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
In certain wireless propagation environments, such as aircraft cabins, the goal of minimizing transmitted power on both the forward link and reverse link is more important than serving a large number of users in a spectrally efficient manner. In that environment, transmit power levels are more important than spectral efficiency because there are a limited number of WCDs and there is a requirement of minimizing the amount of RF energy transmitted due to potential susceptibility of airplane electrical systems. In an aircraft or a similar vehicle, signal propagation is greatly affected by the radio-reflective surface of the interior. The reflections have adverse effects on signal quality, but most WCDs are able to accommodate this. The signal reflections could therefore be ignored as far as ability to communicate with users is concerned, except that it is desired to limit the signal power of transmissions within the vehicle. According to the present invention, a technique that can be implemented for a wireless communication system is used to minimize the transmitted power levels for the terminal and the BTS.
According to the present invention, a microcell is configured to communicate in multiple sectors, with the sectors associated with spatially distributed antennas. Thus, according to one aspect of the invention, the multiple antennas associated with respective sectors exhibit a spatial diversity which is significant with respect to the coverage areas of the sectors. According to another aspect of the invention, the multiple sectors exhibit a significant coverage overlap, but with substantial spatial diversity of the antennas as compared with the coverage areas. According to another aspect of the invention, the antenna separation is a significant factor as compared to the coverage area of the communication sectors of a multiple sector communication station. The antennas are spatially distributed in order to provide multiple communication sectors, with the communication sectors implementing antenna patterns that ensure a large amount of overlap between the sector patterns for a substantial portion of the intended coverage area.
On the reverse link of a CDMA communication system, the signals received at spatially separated antennas can be cabled back to a BTS and coherently combined to result in significantly lower transmitted power requirements at the wireless communication device (WCD). Typically, the combining of the signals is achieved through a “softer handoff” between sectors. Since the propagation environment will often result in significantly different levels of fading between a given wireless communication device (WCD) and the spatially distributed sector antennas, the signal path between the WCD and at least one of the spatially distributed antennas is likely to be of high quality. Power control commands in a CDMA system would tell the WCD to decrease transmitted power in the reverse link until just enough power is being transmitted for successful communication at a reasonable error rate. The “active set” consists of sectors that have been chosen based on their utility to the reverse link demodulation process. On the forward link of IS95, CDMA2000, or WCDMA the signal from a BTS will be transmitted to a user from all sectors in the active set sectors that have been chosen based on their utility to the reverse link demodulation process, using sector specific spreading of the transmitted waveform. The WCD can then coherently combine the signal from each of the transmitting sectors using knowledge of the spreading codes, and since one of the sectors is likely to be received with a good signal quality, the amount of forward link power dedicated to the particular WCD will be decreased based on power control.
The overlapping sectors technique has limitations in terms of capacity of the base station; however in a typical aircraft environment, the number of WCDs is limited. This lowers the C/I on the forward link for the best serving sector since the interference component will include the signals from the other transmitting sectors. Since the overlapping of sectors causes more sectors to be seen by a user, this would limit the forward link data rate for systems such as 1×EV-DV and 1×EV-DO. The forward link capacity is restrained by dimensionality limit due to the finite (e.g 64 or 128) number of orthogonal Walsh codes. In the aircraft environment, it is anticipated that the number of users is small, and so accepting lower capacity is of little consequence. Instead, by the use of multiple sectors, it is possible to enable lower forward link and reverse link transmit power.
The lower transmit power has the effect of reducing noise caused by multiple users. Additionally, to the extent that active radiators are of concern in an aircraft, lowering the transmission power reduces the potential of interference with aircraft nav/comm. equipment.
The passenger cabin 13 is in effect a long tube, which reflects RF transmissions generated within the cabin 13. The communications environment includes a number of users with wireless communication devices (WCDs) 31-38. This presents a unique environment for wireless communications in that transmissions include multiple reflected RF signal components, and the number of WCDs 31-38 is generally limited by the passenger capacity of the aircraft and the average number of WCDs used by each passenger. By way of example, a 100 passenger aircraft will have less than 100 wireless devices on primary (audio) channels and a corresponding number of devices on secondary channels. In addition to the forward bulkhead 17, additional bulkheads 41, 42 and other obstructions 43 are present in the aircraft. This presents a complex communication environment for a communication system whose parameters are established for optimum coverage of large terrestrial areas.
According to the present invention, a base station 51 establishing a picocell provides signals in multiple sectors, which are configured to enhance communication within a confined space. In the case of an aircraft cabin, the base station 51 is located on board the aircraft 11 and has its multiple sectors distributed in a manner such that at least two of the sectors is subject to a substantially different signal propagation path. In terms of the signal characteristics, this provides signal path diversity between sectors.
The representation shows a set of lobes; however the coverage of each lobe extends beyond the boundaries depicted in the diagram. The configuration is such that the antenna patterns of at least two of sectors provide spatial diversity of at least 1λ. The signal overlap is such that communication through the air interface can occur with any of the overlapping sectors in the area of overlap, and provide good quality of service (QoS).
The three antennas 271-273 provide communication through the respective sectors 261-263 and to that extent define the sectors 261-263. The sectors 261-263 are used for both transmit and receive and signals communicated in the sectors 261-263 have different sets of pseudorandom coding. Due to the reflective environment of the cabin 13, the coverage of the sectors 261-263 becomes much less defined than that depicted by the primary lobes.
Since sectors 261-263 are used as part of a common scheme of communication, it is possible for one WCD, for example WCD 33, to communicate in one of the sectors 261-263 and accept a communication handoff to another one of the sectors 261-263. Such a handoff can be a “soft handoff” or a “softer handoff”, in a manner common to inter-sector handoffs, or the handoff can be a “hard handoff”. While these different handoff types imply forward and reverse links, it is possible to provide sector communication in a single direction, such as a reverse link, without sectorizing the other link. It is possible for communication to be effected with a WCD in one sector in the forward link and in a different sector in the reverse link. By way of example, if the system has an inherent imbalance between forward and reverse links, the use of different sectors in the forward and reverse links may be convenient.
It is also possible to use a combination of sectorized and non-sectorized communication. The selection of sectors is generally a function of the WCD, so that the availability of overlapping sectors provides the WCD with the option of selecting from the multiple sectors. For example, in some types of systems it is common to transmit in one sector and receive in all sectors. There are also communications in which it is desired to communicate in one sector but not provide soft handoff and/or softer handoff. Similarly, it is possible to provide a system that uses one handoff scheme in a first type of communication and uses another handoff scheme in a different type of communication.
The arrangement of the antennas 371-373 for the different sectors 361-363 along the length of the cabin provides a substantial degree of spatial diversity, in which the antenna patterns sectors 371-373 provide spatial diversity of greater than 1λ. While it is desirable to provide communication with the different WCDs 31-38 through different sectors 361-363, predetermining the specific sector selected for a specific WCD is not important.
Those skilled in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and algorithms have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, microprocessor, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The methods or algorithms described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a microprocessor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium may be coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal.
In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. For example, one or more elements can be rearranged and/or combined, or additional elements may be added. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
The present Application for Patent claims priority to Provisional Application No. 60/817,945 entitled “WIRELESS COMMUNICATIONS SYSTEM USING SPATIALLY DISTRIBUTED SECTORS IN CONFINED ENVIROMENTS” filed Jun. 30, 2006, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60817945 | Jun 2006 | US |
