Apparatus and method adapted for directional bandwidth reservation with fixed announcement slot in wireless networks

CROSS REFERENCE TO RELATED APPLICATIONS

p-0002The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/035,480, filed Mar. 11, 2008, by Li et al. entitled, “60 GHZ WPAN MAC AND PHY FEATURES”.

BACKGROUND

p-0003The availability of 7 GHz of unlicensed spectrum in the 60 GHz band offers the potential for multi-Gigabit indoor wireless personal area networking (WPAN). Applications that require large bandwidth include uncompressed High Definition (HD) video streaming, fast file download from an airport kiosk (Sync & Go) and wireless display and docking, to name just a few. These applications cannot be supported over existing home networking solutions (IEEE 802.11a/b/g/n and WiMedia UWB) because the required data rates far exceed the capabilities of these networks.

p-0004Thus, a strong need exists for improvements and new development in wireless personal area networks that operate in the 60 GHz band.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0005The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

p-0006<figref idrefs="DRAWINGS">FIG. 1</figref> provides an example of a super-frame schedule of an embodiment of the invention;

p-0007<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a directional bandwidth reservation mechanism of an embodiment of the present invention;

p-0008<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates a directional bandwidth reservation flow according to an embodiment of the present invention; and

p-0009<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates a directional bandwidth reservation mechanism with beam-formed reception according to an embodiment of the present invention.

p-0010It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION

p-0011In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the preset invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

p-0012In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, units and/or circuits have not been described in detail so as not to obscure the invention.

p-0013Although embodiments of the invention are not limited in this regard, discussions utilizing terms such as, for example, “processing,” “computing,” “calculating,” “determining,” “establishing”, “analyzing”, “checking”, or the like, may refer to operation(s) and/or process(es) of a computer, a computing platform, a computing system, or other electronic computing device, that manipulate and/or transform data represented as physical (e.g., electronic) quantities within the computer's registers and/or memories into other data similarly represented as physical quantities within the computer's registers and/or memories or other information storage medium that may store instructions to perform operations and/or processes.

p-0014Although embodiments of the invention are not limited in this regard, the terms “plurality” and “a plurality” as used herein may include, for example, “multiple” or “two or more”. The terms “plurality” or “a plurality” may be used throughout the specification to describe two or more components, devices, elements, units, parameters, or the like. For example, “a plurality of stations” may include two or more stations.

p-0015A mmwave communication link imposes more challenges in terms of link budget than those at lower frequencies (e.g. 2.4 GHz and 5 GHz bands) because of its inherent isolation due to both oxygen absorption, which attenuates the signal over long range, and its short wavelength, which provides high attenuation through obstructions such as walls and ceilings. In many cases, it is preferable to employ directional antennas for high-speed point-to-point data transmission. Devices performing directional transmissions can achieve higher range (mitigation for the link budget issue), as well as better aggregated throughput and spatial reuse, whereas certain pairs of devices separated in space can communicate simultaneously. A directional antenna pattern covering a wide range of angles to give omni-directional coverage is usually employed to aid in neighbor discovery and beam-steering decisions. Furthermore, the antennae supported by devices can be of several types: Non-Trainable Antenna, Sectorized Antenna or Phased Array Antenna.

p-0016In a traditional 60 GHz wireless personal area networks (WPAN) the channel time is scheduled using Time Division Multiple Access (TDMA) technology that does not support parallel transmissions. Channel time reservations are usually performed for each super-frame (the basic timing division for TDMA) by the Coordinator and communicated in the beacon frame as shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, generally as <b>100</b>, with superframe n−1 <b>110</b>, superframe n <b>120</b> and superframe n+1 <b>130</b>. Data channel is illustrated at <b>140</b> and depicts Beacon <b>150</b>, Reserved Channel Time Block (TDMA) <b>160</b> and Unreserved Channel Time Block (CSMA <b>170</b>).

p-0017If a channel time block <b>160</b> is reserved for a specific pair of devices, then the sender performs high-rate directional transmissions. At the same time, if the channel time block is unreserved <b>170</b> it can be accessed using the CSMA (Carrier Sense Multiple Access) mechanism. Unfortunately, the CSMA mechanism necessitates using omni-directional transmissions that are rather inefficient and provide very low throughput. The existing medium access control (MAC) protocols allow reserving channel time blocks only starting from the next super-frame after the new schedule has been announced in the beacon. That incurs large delays for bursty data traffic, which adversely affects the application performance. On the other hand, reserving spare channel time for such traffic leads to poor channel utilization.

p-0018Embodiments of the present invention increase the bandwidth reservation efficiency by using directional transmission. The present invention further increases the throughput and decreases the latency for bursty data traffic and maintains high channel utilization when the channel is shared between bursty and isochronous connections. Embodiments of the present invention also provide efficient spatial reuse, increase the overall throughput of a WPAN and enable power saving for devices since they need to listen to the Coordinator only during the fixed announcement slot.

p-0019Looking now at <figref idrefs="DRAWINGS">FIG. 2</figref>, shown generally as <b>200</b>, the present invention provides a novel mechanism for directional reservation of free channel time blocks using contention-based slots. <figref idrefs="DRAWINGS">FIG. 2</figref> shows reserved channel time block <b>210</b>, unreserved channel time block <b>220</b> and reserved channel time block <b>230</b>. Expanded unreserved channel time block <b>220</b> illustrates contention slot l <b>240</b>, contention slot k <b>250</b>, announcement slot <b>260</b>, allocated reservation period <b>270</b>, unreserved channel time block <b>280</b>. At the beginning of a free time channel time block, there is a pre-defined number k of contention slots used by devices to transmit bandwidth reservation requests to the Coordinator, followed by an announcement slot used by the Coordinator to announce the granted bandwidth reservation if any. A sender that wishes to reserve an unallocated channel time block may select uniformly at random one of the contention slots and transmit a bandwidth reservation request message specifying the requested reservation period using directional transmission pointed towards the Coordinator. The contention slot duration must be long enough to accommodate this transmission. The Coordinator responds to the sender and/or other devices using directional or (quasi) omni-directional transmissions with a bandwidth grant message that specifies the transceiver (also referred to herein as a sender in an embodiment of the present invention) of links and the allocated reservation period, which can be less than or equal to the requested period. If multiple senders (or transceviers) have succeeded with request transmissions, the Coordinator selects one of them. The number k of contention slots can be either fixed (e.g. k=3) or announced by the Coordinator in the beacon frame. The Coordinator may also allow certain non-interfering links to utilize the allocated channel time block as specified in the bandwidth grant message. In this case, the bandwidth grant message must reach all the relevant devices. The message flow of an embodiment of the present invention is shown in <figref idrefs="DRAWINGS">FIG. 3</figref> at <b>300</b>. Sender <b>320</b> sends directional bandwidth request to coordinator <b>330</b> at <b>340</b> and Coordinator <b>330</b> sends BW grant (omni/directional) at <b>350</b>. Sender <b>320</b> transmits data directionally to receiver <b>310</b> at <b>360</b>.

p-0020The present invention works if either beam-formed (directional) or omni-directional antenna is used by the Coordinator for reception during contention slots. However, the Coordinator's reception is susceptible to interference for an omni-directional antenna. At the same time, the bandwidth reservation mechanism may be improved for beam-formed reception. Basically, contention slots are shortened to accommodate only the transmission of a preamble allowing the Coordinator to perform antenna training and lock onto the directional signal. The preamble may be followed by directional transmission of a bandwidth reservation request message. Though the transmission of the request message may collide in time with subsequently transmitted messages, beam-formed reception maximizes the probability that the Coordinator will successfully receive the bandwidth reservation request associated with the first contention slot selected for transmission. Moreover, an additional advantage of this modification is that there is no need for the Coordinator to perform arbitration between multiple received requests since at most one sender can succeed. The modified mechanism for beam-formed reception is presented on <figref idrefs="DRAWINGS">FIG. 4</figref> at <b>400</b> with reserved channel time block <b>410</b>, unreserved channel time block <b>420</b> and reserved channel time block <b>430</b>. Expanded view of unreserved channel time block <b>420</b> illustrates contention frame l <b>450</b>, contention frame k <b>440</b>, announcement clot <b>460</b>, allocated reservation period <b>470</b> and unreserved channel time block <b>480</b>.

p-0021In embodiments of the present invention, two extensions may be added. Firstly, a bandwidth reservation request message may ask for a time period longer than the available time in the unallocated channel time block under consideration and the Coordinator may reserve to the sender the difference between the requested time and the actually allocated time in the future without a need to send an extra bandwidth reservation request. Secondly, if the number of devices in the WPAN that generate bursty traffic does not exceed the number of contention slots, then the Coordinator may associate every such device with a dedicated contention slot by making an advertisement in the beacon frame, thereby removing contention.

p-0022While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.