Patent Publication Number: US-2009238118-A1

Title: Reducing cost of cellular backhaul

Description:
RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 11/148,953, filed on Jun. 9, 2005, which claims priority to U.S. Provisional Application No. 60/578,266, filed Jun. 9, 2004. The above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The following description relates to radio systems. 
     BACKGROUND 
     In cellular systems today, voice, data and signaling traffic must be backhauled from the cell tower sites to the central office where the mobile switching center is located. In general, backhauling refers to getting data to the core network, e.g., between the base station and the base station controller. In some cases, backhauling may include sending network data over an out-of-the-way route (including taking it farther than its destination) in order to get the data to its destination sooner or at a lower cost. Currently, a majority of this backhaul takes place over dedicated T1 lines. There are also some wireless backhaul schemes used primarily in short range niche applications that utilize both licensed and unlicensed bands. 
     Cellular backhaul primarily utilizes dedicated T1 lines. The guaranteed bandwidth and latency are important to support real time voice calls. Typically, T1 slots are dedicated to particular voice circuits or data channels. Bandwidth efficiencies of using IP over the backhaul to aggregate traffic and dynamically adapt capacity to the varying demand for data and voice are available, but are not used in the majority of deployments today. 
     While there are several wireless backhaul technologies, the interface to these systems is typically made to look like a T1 line. This allows the same interfaces and time slot assignments to be used. The advantage of wireless backhaul is lower cost compared to leasing T1 lines, but the wireless systems are often limited in range and by terrain. 
     There has been interest in using the public Internet to backhaul cellular traffic given the wide availability and relatively low cost of Internet connections compared with dedicated T1 lines. 
     SUMMARY 
     In some aspects, the invention includes a method for backhauling wireless voice and data transmissions. The method includes receiving, at a base station, a wireless transmission. 
     The method also includes forwarding the transmission from the base station to a base station controller over a shared network. 
     Embodiments can include one or more of the following. 
     The method can include receiving, at the base station controller, a second transmission and forwarding the second transmission to the base station over the shared network. The shared network can be a non-private network. The shared network can be the Internet. 
     The method can also include providing a jitter buffer at the base station controller and using the jitter buffer to compensate for jitter introduced by the shared network. The method can also include providing a jitter buffer at the base station and using the jitter buffer to compensate for jitter introduced by the shared network. 
     Forwarding the transmission can include forwarding the transmission using a secure protocol. The secure protocol can be SSL. 
     The method can also include determining a priority of the received transmission and forwarding the transmission based on the determined priority. Determining a priority can include assigning a first priority to voice transmissions and assigning a second priority to data transmissions. The first priority can be greater than the second priority. 
     Forwarding the transmission can include forwarding the transmission using voice over IP technology. The method can also include performing decryption of the transmission at the base station controller. The method can also include performing encryption of the second transmission at the base station controller. The method can also include performing power control at the base station. The transmission can be a transmission from a cellular telephone. 
     In additional aspects, the invention includes a method that includes receiving, at a base station, a wireless transmission from a first mobile unit to be routed to a second mobile unit. The method also includes determining if the second mobile unit is within a communication range of the base station and if the second mobile unit is within the range, locally routing the transmission from the first mobile unit to the second mobile unit at the base station. 
     Embodiments can include one or more of the following. 
     The method can include forwarding the transmission from the base station to a base station controller if the second mobile unit is not within the range. Forwarding the transmission from the base station to the base station controller can include forwarding the transmission from the base station to the base station controller over a shared network. The shared network can be the Internet. 
     In additional aspects, the invention includes a system for backhauling wireless voice and data transmissions. The system includes a base station configured to receive a wireless transmission and forward the transmission to a base station controller over a shared network. 
     Embodiments can include one or more of the following. 
     The system can also include a base station controller configured to receive a second transmission and forward the second transmission to the base station over the shared network. The shared network can be the Internet. The base station controller can include a jitter buffer configured to compensate for jitter introduced by the shared network. The base station can include a jitter buffer configured to compensate for jitter introduced by the shared network. The base station can be further configured to determine a priority of the received transmission and forward the transmission based on the determined priority. 
     In additional aspects, the invention includes a system that includes a base station. The base station is configured to receive a wireless transmission from a first mobile unit to be routed to a second mobile unit and determine if the second mobile unit is within a communication range of the base station. If the second mobile unit is within the range, the base station is configured to locally route the transmission from the first mobile unit to the second mobile unit at the base station. 
     Embodiments can include one or more of the following. 
     The system can also include a base station controller. The base station can be configured to forward the transmission to the base station controller if the second mobile unit is not within the range. 
     Advantages that can be seen in particular implementations include one or more of the following. 
     In some embodiments, using a software radio system can reduce the cost of cellular backhaul. 
     In some embodiments, the software radio system allows one to perform rapid experiments and any changes to the system or protocol can be software downloads to the infrastructure. 
     In some embodiments, the software radio system employs QoS measurements and mechanisms to ensure adequate bandwidth and latency to support voice and data user requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of a network. 
         FIG. 1B  is a block diagram of a network. 
         FIG. 2  is a block diagram of a network. 
         FIG. 3  is a block diagram of a network. 
         FIG. 4  is a flow chart. 
         FIG. 5  is a block diagram of a network. 
         FIG. 6  is a block diagram of a network. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , a system  10  includes a mobile unit  12  and a base station  14 . The base station is connected to the Internet  16  close to the backbone and routs cellular traffic to the core network of a cellular service provider with lightweight, QoS mechanisms in place. The QoS mechanisms provide the required level of service for system  10  such that the system does not rely on the existence of excess bandwidth to provide the required level of service. 
     More particularly, system  10  includes a mobile unit  12  which sends wireless signal transmissions to a base station  14 . The base station  14  routs the transmissions to a base station controller  18  over the Internet  16  (e.g., the public Internet). The base station controller  18  subsequently routs the calls to the mobile switching unit  20  and the mobile switching unit  20  routs the calls to the public switched telephone network  22 . In some embodiments, the signal transverses a second network (e.g., Internet  24 ) which is disposed between the base station controller  18  and the mobile switching unit  20  ( FIG. 1B ) 
     Signals can also be sent from the public switched telephone network  22  to the mobile unit  12  via the mobile switching unit  20 , base station controller  10 , Internet  16 , and base station  15 . 
     Software radios can aid in the characterization of performance of the public Internet  16  for backhauling real-time cellular voice and data traffic. Various types of QoS measurements and mechanisms can be used to support such real-time cellular voice and data traffic. 
     In order to reduce the cost of cellular backhaul, it is useful to use the Internet. At this point in time, one of the easiest ways to assure a high level of Internet service is to connect devices close to the backbone. The location of the device relative to the backbone avoids a portion of the additional hops and constrained bandwidth at the edges of the network. The excess bandwidth in the backbone of the Internet  16  today, a result of overbuilding fiber in the core, can generally support the QoS requirements for cellular traffic. However, as users demand services in remote locations, more hops are typically required to provide services in those locations and QoS deteriorates. Similarly, when extraordinary traffic is experienced in the core network, even the current excess bandwidth may not provide adequate resources to efficiently meet demand. 
     Various protocols can be used to provide efficiency and bandwidth optimization. Exemplary protocols include TCP, UDP and RTP, as well as end-to-end application level QoS protocols implemented on top of these protocols. 
     In some embodiments, existing devices on the public Internet  16  can be used to rout the calls from the mobile unit  12  to the public switched telephone network  22  using the public Internet for backhaul without requiring the deployment of new routers or other hardware in the network. This enables use of the Internet for backhaul on a much more rapid timescale. It is believed that such an implementation will result in significant cost savings for wireless carriers today. 
     Referring to  FIG. 2 , an exemplary routing of a call over the Internet  36  is shown. In this example, base stations located in Texas  32  and Cambridge  34 , connected via the public Internet  36  to mobile switching center  38  in Vancouver. Table 1 shows the number of hops between the base station  34  located in Cambridge and the switch  38  in Vancouver, and Table 2 shows the hops between the base station  32  located in Texas and the switch  38  in Vancouver. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Traceroute to 207.23.93.38 from Cambridge, 30 hops max, 38 byte packets 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 pos 
                 (192.168.0.1) 
                 0.436 
                 ms 
                 0.291 
                 ms 
                 0.211 
                 ms 
               
               
                 2 
                 w225.z064221090.bos- 
                 (64.221.90.225) 
                 1.062 
                 ms 
                 0.872 
                 ms 
                 0.877 
                 ms 
               
               
                   
                 ma.dsl.cnc.net 
               
               
                 3 
                 208.177.193.1.ptr.us.xo.net 
                 (208.177.193.1) 
                 146.914 
                 ms 
                 200.582 
                 ms 
                 168.402 
                 ms 
               
               
                 4 
                 ge5-00.MAR2.Cambridge- 
                 (207.88.86.53) 
                 170.937 
                 ms 
                 204.480 
                 ms 
                 187.509 
                 ms 
               
               
                   
                 MA.us.xo.net 
               
               
                 5 
                 p5-1-0-2.RAR2.NYC- 
                 (65.106.3.33) 
                 204.374 
                 ms 
                 87.548 
                 ms 
                 95.330 
                 ms 
               
               
                   
                 NY.us.xo.net 
               
               
                 6 
                 p1-0.IR1.NYC- 
                 (65.106.3.42) 
                 111.932 
                 ms 
                 113.313 
                 ms 
                 181.227 
                 ms 
               
               
                   
                 NY.us.xo.net 
               
               
                 7 
                 206.111.13.18.ptr.us.xo.net 
                 (206.111.13.18) 
                 132.570 
                 ms 
                 148.973 
                 ms 
                 98.475 
                 ms 
               
               
                 8 
                 core1-newyork83-pos0- 
                 (206.108.103.177) 
                 20.721 
                 ms 
                 127.483 
                 ms 
                 148.096 
                 ms 
               
               
                   
                 3.in.bellnexxia.net 
               
               
                 9 
                 core4-montrea102-pos6- 
                 (206.108.99.189) 
                 133.495 
                 ms 
                 314.225 
                 ms 
                 248.051 
                 ms 
               
               
                   
                 3.in.bellnexxia.net 
               
               
                 10 
                 64.230.243.238 
                 (64.230.243.238) 
                 269.619 
                 ms 
                 93.072 
                 ms 
                 94.338 
                 ms 
               
               
                 11 
                 core1-vancouver-pos10- 
                 (64.230.229.38) 
                 93.456 
                 ms 
                 106.692 
                 ms 
                 93.993 
                 ms 
               
               
                   
                 2.in.bellnexxia.net 
               
               
                 12 
                 dis4-vancouver-pos6- 
                 (206.108.101.66) 
                 92.230 
                 ms 
                 91.601 
                 ms 
                 91.677 
                 ms 
               
               
                   
                 0.in.bellnexxia.net 
               
               
                 13 
                 69.156.254.254 
                 (69.156.254.254) 
                 104.744 
                 ms 
                 104.470 
                 ms 
                 103.289 
                 ms 
               
               
                 14 
                 blnt1-vlan2.hc.BC.net 
                 (207.23.240.232) 
                 102.966 
                 ms 
                 104.999 
                 ms 
                 103.303 
                 ms 
               
               
                 15 
                 telostech2.BC.net 
                 (134.87.24.62) 
                 170.350 
                 ms 
                 128.600 
                 ms 
                 120.643 
                 ms 
               
               
                 16 
                 134.87.54.6 
                 (134.87.54.6) 
                 115.420 
                 ms 
                 132.120 
                 ms 
                 111.732 
                 ms 
               
               
                 17 
                 207.23.93.38 
                 (207.23.93.38) 
                 111.607 
                 ms 
                 127.547 
                 ms 
                 125.545 
                 ms 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Traceroute to 207.23.93.38 from MidTex, 30 hops max, 38 byte packets 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 com-sa-1.cctc.net 
                 (208.6.233.1) 
                 0.276 
                 ms 
                 7.027 
                 ms 
                 0.262 
                 ms 
               
               
                 2 
                 sl-gw30-fw-1-1-0- 
                 (144.228.139.237) 
                 235.334 
                 ms 
                 17.840 
                 ms 
                 10.711 
                 ms 
               
               
                   
                 TS24.sprintlink.net 
               
               
                 3 
                 sl-bb23-fw-2- 
                 (144.232.12.174) 
                 8.653 
                 ms 
                 46.239 
                 ms 
                 19.150 
                 ms 
               
               
                   
                 0.sprintlink.net 
               
               
                 4 
                 sl-bb25-chi-6- 
                 (144.232.9.25) 
                 37.363 
                 ms 
                 37.972 
                 ms 
                 37.075 
                 ms 
               
               
                   
                 0.sprintlink.net 
               
               
                 5 
                 sl-bb21-sea-1- 
                 (144.232.20.156) 
                 77.978 
                 ms 
                 73.554 
                 ms 
                 73.691 
                 ms 
               
               
                   
                 0.sprintlink.net 
               
               
                 6 
                 sl-gw11-sea-8- 
                 (144.232.6.118) 
                 119.849 
                 ms 
                 73.350 
                 ms 
                 73.333 
                 ms 
               
               
                   
                 0.sprintlink.net 
               
               
                 7 
                 sl-teleg-4- 
                 (160.81.36.14) 
                 82.840 
                 ms 
                 74.541 
                 ms 
                 74.457 
                 ms 
               
               
                   
                 0.sprintlink.net 
               
               
                 8 
                 core2-seattle-pos0- 
                 (206.108.102.197) 
                 74.743 
                 ms 
                 87.826 
                 ms 
                 74.935 
                 ms 
               
               
                   
                 1.in.bellnexxia.net 
               
               
                 9 
                 core2-vancouver- 
                 (206.108.102.210) 
                 83.550 
                 ms 
                 91.493 
                 ms 
                 78.653 
                 ms 
               
               
                   
                 pos10- 
               
               
                   
                 1.in.bellnexxia.net 
               
               
                 10 
                 dis4-vancouver- 
                 (206.108.101.70) 
                 99.620 
                 ms 
                 78.485 
                 ms 
                 159.792 
                 ms 
               
               
                   
                 pos9- 
               
               
                   
                 0.in.bellnexxia.net 
               
               
                 11 
                 69.156.254.254 
                 (69.156.254.254) 
                 78.796 
                 ms 
                 78.648 
                 ms 
                 78.711 
                 ms 
               
               
                 12 
                 blnt1- 
                 (207.23.240.232) 
                 82.164 
                 ms 
                 81.627 
                 ms 
                 78.636 
                 ms 
               
               
                   
                 vlan2.hc.BC.net 
               
               
                 13 
                 Telostech2.BC.net 
                 (134.87.24.62) 
                 87.021 
                 ms 
                 100.408 
                 ms 
                 84.433 
                 ms 
               
               
                 14 
                 134.87.54.6 
                 (134.87.54.6) 
                 97.545 
                 ms 
                 88.719 
                 ms 
                 101.795 
                 ms 
               
               
                 15 
                 207.23.93.38 
                 (207.23.93.38) 
                 136.840 
                 ms 
                 110.697 
                 ms 
                 98.773 
                 ms 
               
               
                   
               
            
           
         
       
     
     As shown in tables 1 and 2 above, routing the call utilizing the available Internet connections can provide adequate quality of service. It is noted that the number and contribution of the hops towards the edge of the network comprise a significant portion of the delay. Therefore, it is believed that with a connection closer to the Internet backbone or other public network of a data network service provider, there may be enough excess bandwidth to consistently meet the cellular backhaul QoS requirements with no QoS protocols or lightweight QoS protocols. 
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Traceroute to vanu-bsc.dyn.nimlabs.org (24.239.114.151), 
               
               
                 30 hops max, 38 byte packets: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 * * * (internal 
                   
                   
                   
                   
               
               
                   
                 network node) 
               
               
                 2 
                 * * * (internal 
               
               
                   
                 network node) 
               
               
                 3 
                 acs-24-239-114- 
                 (24.239.114.151) 
                 25.417 ms 
                 26.531 ms 
                 34.788 ms 
               
               
                   
                 151.zoominternet.net 
               
               
                 4 
                 acs-24-239-114- 
                 (24.239.114.151) 
                 25.561 ms 
                 20.253 ms 
                 52.069 ms 
               
               
                   
                 151.zoominternet.net 
               
               
                   
               
            
           
         
       
     
     As shown in table 3 above, routing the call utilizing the available Internet connections can provide adequate quality of service. The voice is transmitted using the RTP protocol, and there is potential backhaul bandwidth savings through the use of RTP header compression. This use of IP and other standard Internet protocols provides a smooth path to transitioning to Internet-based backhaul. It is noted that placing the base station near the Internet reduces the number of hops. The impact on number of hops and total latency of transmission is significant. Placing the base station near the Internet backbone (thereby reducing the number of hops) can reduce the latency and ensure a higher level of QoS for voice transmission. 
     While the Internet  36  typically provides excess bandwidth capable of providing adequate QoS, additional routing procedures and features may be used to provide the adequate QoS during loaded or crisis situations. 
     As described above, the use of multiple hops between the base station and the base station controller can increase the signal latency. For example, a typical Internet connection goes through several hops and bandwidth constrained links at the edge of the network. These edge routers and links are a major contributor to the overall bandwidth and latency of the connection. ISP&#39;s may choose to charge a higher fee to connect close to the backbone, but it is likely that this fee will still be much lower than T1 costs today which can range from $400-$2,000 per month, depending upon location and distance. 
     In order to test the operability of replacing T1 lines with a communication path utilizing the Internet, various testing has been completed. A typical connection between a base station and base station controller using existing T1 lines can be used to measure the baseline bandwidth, latency and jitter for comparison purposes. The traffic load was generated by standard GSM mobiles, wirelessly connected to the software radio base station. The T1 connections were replaced with public Internet connections (e.g., as shown in  FIG. 1A ). The effective bandwidth latency and jitter were measured using similar load conditions as the baseline experiment. 
     Due to the unpredictable variation in use of the public Internet, various types of application level QoS and failure recovery are desirable, although service without QoS mechanisms is also possible. In many real-time systems, TCP-style re-transmission is not appropriate, since the data will be too old by the time it is re-transmitted. Other approaches involve embedding error correction into the data stream so that lost packets can be reconstructed, or rules for dropping or repeating packets in the event of a loss. The most important parameter is keeping the call alive. In cellular systems, callers are accustomed to occasional drop outs or degradation in voice quality, but a dropped call is a significant problem. The recovery mechanism must insure that the mobile unit does not determine that the call has been dropped and terminate the connection. 
     As described above, various QoS mechanisms can be used to ensure the latency and quality of the signal transmitted from the mobile unit  12  to the public switched telephone network  22  over the Internet  16 . Since the Internet  16  is a shared network it can be beneficial to use various techniques to ensure that the QoS is maintained such that there is not an interruption in the voice service for the customer. 
     In some embodiments, admission control can be used in data networks to insure a smooth flow of call data during times of extreme load in the network. In this case, the system would be making a quality/capacity tradeoff, supporting fewer voice calls but maintaining minimum quality standards. 
     Referring to  FIG. 3 , a system  70  includes multiple mobile units  72 ,  74 , and  76  and a base station  78 . In operation, the mobile units  72 ,  74 , and  76  generate signals and rout calls through the base station  78  to a base station controller and telephone network over the Internet. Due to the variability of the bandwidth available on the shared network, the base station  78  can limit the number of mobile units and additional users for which the base station will concurrently process and rout the voice calls. If the Internet is busy or does not have available bandwidth to ensure a predicted QoS, the base station  78  will reject the transmission from one or more of the mobile units. 
     Referring to  FIG. 4 , a process for insuring a QoS for a call during times of extreme load in the network is shown. The base station monitors and determines  82  an available bandwidth of the shared network. For example, the base station can ping another device on the network and monitor the response time for the ping packet. While using a ping packet does not provide a precise measurement of bandwidth, it can be used as a metric to determine if there is enough bandwidth available to ensure a particular level of quality for a voice call routed over the network. Based on the measured bandwidth, the base station determines  88  if there is enough bandwidth to support the voice call. If there is enough bandwidth, then the base station routs  90  the call through the base station over the Internet to the base station controller. If there is not enough bandwidth, then the base station blocks  86  the call such that the call is not routed over the Internet to the base station controller. 
     Referring to  FIG. 5 , a system  100  including multiple mobile units  102 ,  104 ,  106 , and  108  and a base station  118  is shown. In operation, the mobile units  102 ,  104 ,  106 , and  108  rout signals through the base station  118  to a base station controller. The mobile units  102 ,  104 ,  106 , and  108  can rout both voice and data over the network. For example, mobile units  102 ,  106 , and  108  are shown as transmitting voice data  110 ,  114 , and  116  which mobile unit  104  is shown transmitting data  112 . In general, the latency required for voice transmissions to ensure a desired quality level is lower than the latency required for a data transmission. Due to the variability of the bandwidth available on the shared network, the base station  118  can shift the transmission time for some transmissions in order to account for the bandwidth of the network. For example, if the network is at or near capacity, the base station  118  can delay the transmission of the data transmissions by a predetermined time, e.g., about 1 to 3 seconds. The shifting of the transmission time for data transmissions based on the available bandwidth allows users to more effectively use the bandwidth available on the shared network. 
     In some embodiments, the shared network can include a guaranteed bandwidth for a particular user. For example, if the network supports dedication of bandwidth, the base station can be allocated a sufficient bandwidth to ensure a particular level of quality for the transmission of calls. 
     In some embodiments, the system can include a jitter buffer at one or both ends of the backhaul link to compensate for jitter in the shared network. In general, signal processing systems include some jitter which is a random variation in the time required to complete any particular task. At the lowest levels of the system, the jitter is due to hardware effects, such as the relative time at which two chips request access to a shared bus. At higher levels, the jitter comes from variable and unpredictable network performance. The jitter buffers can ensure that the system will continue to process signals and present them to the system users in accordance with the relevant communications protocol even when significant jitter exists in the network. 
     In some embodiments, the use of software based radios can allow the functionality of the base station and the base station controller to be allocated as desired. For example, in a cellular link, the encryption/decryption of the data can be moved to the back end (e.g., the base station controller) side of the link. In addition, other functionality typically executed in the base station controller (e.g., power control) can be moved to the front end (e.g., the base station) of the link. 
     One exemplary re-distribution of functionality between the base station and the base station controller is shown in  FIG. 6 . A system  130  includes multiple mobile units  132  and  134 , a base station  136 , and a base station controller  140 . During typical operation, certain switching operations occur at the base station controller. Therefore, if a mobile unit  132  desired to call mobile unit  134 , the transmission would travel from mobile unit  132  to the base station  136  and across network  138  to the base station controller  140 . This transmission can introduce latency in the transmission. In addition, the transmission will require a portion of the bandwidth of network  138 . In a software based system, some of the switching functionality can be moved from the base station controller  140  to the base station  136 . For example, the base station  136  can determine if a call is being routed to a callee on the same base station and if so then the call can be routed at the base station. Routing such calls locally at the base station reduces the backhaul bandwidth because the call never transverses network  138 . 
     While in some of the embodiments described above, a QoS mechanism is used, other embodiments exist in which a QoS mechanism is not implemented. 
     There has been described novel apparatus and techniques for reducing the cost of cellular backhaul. It is evident that those skilled in the art may now make numerous modifications and uses of and departures from specific apparatus and techniques herein disclosed without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims. 
     Other implementations are within the scope of the following claims: