Abstract:
Overlay handover is generally presented. In this regard, a method is introduced including storing a broadband wireless network composite signal in a sample buffer, processing the sample buffer using subcarriers associated with a serving base station to determine a bandwidth grant from a first MAP, and reprocessing the sample buffer using subcarriers associated with a neighboring co-channel base station to determine a bandwidth grant from a second MAP. Other embodiments are also described and claimed.

Description:
CLAIM OF PRIORITY 
     The present application claims priority to provisional application 61/134,188 filed on Jul. 7, 2008. 
    
    
     FIELD 
     Embodiments of the present invention may relate to the field of broadband wireless network handovers, and more specifically to an overlay handover in a broadband wireless network. 
     BACKGROUND 
     Broadband wireless handover (HO) is a key mobility feature that is especially important for voice and video services. Voice/Video performance is a very important factor in customer satisfaction and viability of the network business model. It is very important not to have significant transport data flow interruptions during the handover process. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention may become apparent from the following detailed description of arrangements, example embodiments, and the claims when read in connection with the accompanying drawings. While the foregoing and following written and illustrated disclosure focuses on disclosing arrangements and example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and embodiments of the invention are not limited thereto. 
    
    
     
       The following represents brief descriptions of the drawings in which like reference numerals represent like elements and wherein: 
         FIG. 1  is a block diagram of an example overlay wireless broadband network, in accordance with one example embodiment of the invention; 
         FIG. 2  is a block diagram of an example carrier frequency assignment, in accordance with one example embodiment of the invention; 
         FIG. 3  is a flow diagram of an example interruption free overlay handover, in accordance with one example embodiment of the invention; and 
         FIG. 4  is a block diagram of an example co-frame processing, in accordance with one example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that embodiments of the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
       FIG. 1  is a block diagram of an example overlay wireless broadband network, in accordance with one example embodiment of the invention. Wireless broadband network  100  is intended to represent a broadband wireless network that supports mobile devices. In one embodiment, wireless broadband network  100  complies with a revision of the IEEE 802.16 standard, for example IEEE standard 802.16e-2005. In accordance with the illustrated example embodiment, wireless broadband network  100  may include one or more of mobile station  102 , base stations  104 ,  106  and  108 , base station ranges  110 ,  112  and  114 , and network backbone  116  coupled as shown in  FIG. 1 . 
     Mobile station  102  represents any mobile device that connects to wireless broadband network  100 . For example, mobile station  102  may represent, but it not limited to, a laptop, netbook, cell phone, mobile internet device, tablet, personal data assistant, etc, with wireless broadband capabilities and access. Mobile station  102  may travel with a user such that mobile station  102  becomes further away from some base stations and closer to other base stations. 
     Base stations  104 ,  106  and  108  provide wireless broadband network access to mobile stations, such as mobile station  102 . Base stations  104 ,  106  and  108  may, for example, represent base stations with large antenna on tower, small antenna on buildings, or very small antenna in electronic devices. Base stations  104  may represent a macro-cell, with base stations  106  and  108  serving as overlay cells (such as relay, pico or femto cells), though the present invention is not so limited. In one embodiment, base stations  104 ,  106  and  108  share a single channel of bandwidth around a center frequency (intra-frequency-assignment or intra-FA) and operate with a frequency reuse of 3. In another embodiment, base station  104 ,  106  and  108  use separate channels of bandwidth around their individual center frequencies and operate in inter-frequency-assignment (inter-FA) deployment. Base stations  104 ,  106  and  108  may communicate with each other through network backbone  116 , which may represent a wired network connection. In one embodiment, base stations  104 ,  106  and  108  communicate with each other over network backbone  116  to negotiate bandwidth access for mobile stations, for example as part of a handover as described in more detail hereinafter. Base stations  104 ,  106  and  108  may also know the location of neighboring base stations and may determine an appropriate base station to which to handover a mobile station based on data from the mobile station. 
     Base station ranges  110 ,  112  and  114  represent a signal range from base stations  104 ,  106 , and  108 , respectively. In one embodiment, base station ranges  110 ,  112  and  114  represent the range to which the associated base station provides acceptable signal strength, though the signals may be detectable at greater ranges. Though not shown, greater signal strengths may exist at ranges closer to the base stations. 
       FIG. 2  is a block diagram of an example carrier frequency assignment, in accordance with one example embodiment of the invention. Frequency assignment  200  may include spectrum  202 , macro-cell subcarrier  206 , relay-cell subcarrier  208 , pico-cell subcarrier  210 , and femto-cell subcarrier  212 , as shown. Spectrum  202  represents the radiation frequencies used for wireless broadband network  100 , and may be assigned by governmental agencies. While shown as being centered around 2.5 GHz with a bandwidth of 20 MHz, other frequencies and other bandwidths, for example less than 1 GHz or greater than 3 GHz, may be used. In one embodiment, subcarriers deployed in a same location as part of an inter-FA overlay may include macro-cell subcarrier  206 , relay-cell subcarrier  208 , pico-cell subcarrier  210 , and femto-cell subcarrier  212 , which may be associated with any of base stations  104 ,  106  and  108 . In another embodiment, base stations  104 ,  106  and  108  may use fractions of macro-cell subcarrier  206  (i.e., subcarriers  206 A,  206 B and  206 C) representing an intra-FA (or co-channel) overlay. Communication of the subcarriers used by the base stations may occur over network backbone  116 . 
       FIG. 3  is a flow diagram of an example interruption free overlay handover, in accordance with one example embodiment of the invention. In this example, mobile station  102  is currently being served by base station  104 , but is moving toward base station  106 , which could necessitate a handover. Flow  300  may start with mobile station  102  receiving ( 302 ) information about neighboring base stations  106  and  108  from serving base station  104 . In one embodiment, serving base station  104  may provide mobile station  102  with subcarrier assignments for base stations  106  and  108 . At some time, mobile station  102  may find ( 304 ) and perform scanning ( 306 ) to determine existence of co-channel base stations and to determine signal strength and quality. Mobile station  102  determines the existence of co-channel base stations  106  and  108  using the neighbor information from serving base station  104 . In one embodiment a scan involves: mobile station  102  collects signal samples and processes using serving base station  104  subcarrier; mobile station  102  temporarily saves signal samples (enough for processing co-channel subcarriers); mobile station  102  re-processes signal samples using base station  106  (which may become target base station, TBS) subcarrier; mobile station  102  determines signal strength and quality; mobile station  102  re-processes signal samples using base station  108  subcarrier; mobile station  102  determines signal strength and quality. During this scan processing, mobile station  102  (MS) continues to process the serving base station  104  (SBS) frame as usual. 
     Handover (HO) is triggered either by the MS or the SBS. For MS-initiated HO, MS determines the possibility of an overlay handover based on scanning. For BS-initiated HO, SBS determines the possibility of an overlay handover using the scan results provided by the MS. SBS negotiates ( 308 ) with one or more TBSs for HO start frame, MS identification update, and pre-allocated SBS/TBS bandwidth grants for MS. For intra-FA overlay HO, The SBS and TBS may agree on non-overlapping uplink bandwidth allocations, while downlink bursts may or may not overlap. For inter-FA overlay HO, both downlink bursts and uplink bandwidth allocations may or may not overlap. There are options for MS resource grants during HO depending on MS capabilities. For intra-FA overlay HO, MS co-frame processing is required for overlap downlink bursts. For inter-FA overlay HO, MS dual radio co-frame processing is required for overlap downlink/uplink bursts. In one embodiment, if the MS is capable of processing both the SBS and TBS DL-MAP and UL-MAP in time to receive and transmit to the SBS and TBS (as shown in  FIG. 4 ), then dynamic bandwidth grants (specified in MAPs) can be used, otherwise bandwidth grants during HO may be static (specified before HO). 
     SBS then sends ( 310 ) a handover response to MS. MS then sends ( 312 ) HO-IND message to SBS and SBS sends ( 314 ) HO confirmation to TBS. HO then starts ( 316 ). Co-frame processing ( 318 ) and SBS/TBS messaging ( 320 ) may be repeated several times before HO is complete ( 322 ) and TBS ( 106 ) becomes the serving base station. 
       FIG. 4  is a block diagram of an example co-frame processing, in accordance with one example embodiment of the invention. Composite signal  400  includes MS sample buffer  402 , SBS frame  404 , TBS frame  406 , SBS preamble  408 , TBS preamble  410 , preamble offset  412 , SBS MAPS  414 , TBS MAPS  416 , MS SBS downlink  418 , MS TBS downlink  420 , MS SBS uplink  422  and MS TBS uplink  424 . An MS receives a composite signal composed of the signal from the Serving Base Station (SBS), i.e. SBS frame  404 , and signals from neighboring BSs, i.e. TBS frame  406 , on the co-channel and stores them in MS sample buffer  402 , which may be processed iteratively to extract data from both SBS frame  404  and TBS frame  406 . 
     Mobile station  102  may use subcarrier information previously received to find TBS preamble  410 , which may be separated in time from SBS preamble  408  by preamble offset  412 . Mobile station  102  may then read SBS MAPS  414  and TBS MAPS  416  to determine the bandwidth grants of MS SBS downlink  418 , MS TBS downlink  420 , MS SBS uplink  422  and MS TBS uplink  424 . MS SBS uplink  422  and MS TBS uplink  424  would have been previously negotiated by SBS and TBS to be non-overlapping. In this way MS could receive downlink from and send uplink to both SBS and TBS in a same frame. In one embodiment, as part of a handover process mobile station  102  may send transport data to base station  104  and control information to base station  106  within a same frame. In another embodiment, mobile station  102  may concurrently send and/or receive transport data to/from both base station  104  and base station  106 . 
     Although embodiments of the present invention have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention. More particularly, reasonable variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the foregoing disclosure, the drawings and the appended claims without departing from the spirit of the invention. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.