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5G Carrier Grade Wi-Fi: Addressing the Needs for Uplink Throughput, Dense Deployments and Cellular-like Quality
Research Paper / Nov 2014 / 5G, CGW

The Future of Wi-Fi Promises up to a 4-Fold Capacity Improvement

Mobile data traffic is growing at an annual rate of more than 60%, and Wi-Fi usage is already 20x greater than cellular systems for wireless data delivery. With more and more demand for Wi-Fi services, the industry is looking toward next generation, Carrier Grade Wi-Fi (CGW), systems. At InterDigital, we’re looking even further ahead – to 5G CGW, a solution that may deliver up to 4 times the capacity of existing Wi-Fi services. Probable requirements as well as some candidate technologies are addressed including: Multi-User Parallel Channel Access (MU/PCA), Fractional CSMA (FCSMA),Transmit Power Control (TPC), and Uplink Multi-User MIMO (UL MU-MIMO). Download the full white paper to read more about InterDigital’s vision for 5G Carrier Grade Wi-Fi.

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SolutionsWhite Paper 5G Carrier Grade Wi-Fi: Addressing the Needs for Uplink Throughput, Dense Deployments and Cellular-like Quality The Future of Wi-Fi Promises Up to 4-Fold Capacity Improvement Published July, 2014 5G Carrier Grade Wi-Fi | 2 Contents Executive Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The Growth of Mobile Data Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Mobile Application Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 IEEE Wi-Fi Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5G CGW Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5G CGW Candidate Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Multi-User Parallel Channel Access (MU/PCA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Fractional CSMA (FCSMA) and Transmit Power Control (TPC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Uplink Multi-User MIMO (UL MU-MIMO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Next Steps: Collaboration with Industry and University Partners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Further Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5G Carrier Grade Wi-Fi | 3 Executive Overview Carrier Grade Wi-Fi (CGW) is widely seen in the telecom industry as the next generation enhancement to Wi-Fi. It will drive the focus of the IEEE 802.11ax Task Group (TGax), formerly the High Efficiency WLAN Study Group (HEW SG), for enhancing wireless system throughput and area coverage in high density Access Point (AP) and Station (STA) deployments. Wi-Fi already accounts for 40% of all data delivery with wireless systems, which is 20 times greater than data delivery over cellular systems.1 Overall, Wi-Fi is expected to increase exponentially through 2017, mostly through growth in public Wi-Fi locations (Figure 1) and the existing Wi-Fi dominance for indoor home and enterprise use. The recently ratified Wi-Fi technology standard, IEEE 802.11ac, is foreseen as inadequate for 5G CGW requirements, specifically in the areas of uplink throughput, deployment density and cellular-like quality . This paper provides an overview of InterDigital?s vision for addressing 5G CGW requirements (Figure 2). Leveraging InterDigital?s years of Wi-Fi experience, the solutions described can achieve four to six times the capacity of the 802.11ac standard with cellular-like quality. As 5G CGW moves towards reality, InterDigital looks forward to collaborating with industry and university partners to transition its 5G technology from concepts to reference platforms to deployed products. 1 ?Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update?, 2012?2017 Source: Cisco VNI Global Mobile Data Traffic Update, 2012-2017 Source: InterDigital 2008 2009 2010 2011 2012 Worldwide public Wi-Fi loca?ons: 2008-2012 820,262 682,929 414,356 289,476 237,507 In response to exponential Wi-Fi growth, InterDigital is addressing 5G Carrier Grade Wi-Fi requirements. ? Signaling efficiency with large number of users ? Increased spectral efficiency especially on the uplink when APs operate on the same frequency ? Coopera?on between APs to improve spa?al efficiency and area throughout ? Scheduling support to provide air?me fairness and focus on cell-edge throughout performance ? Power Efficiency (sleep modes) ? Robustness to interference (OBSS management) ? Power Control to adapt to deployment densi?es ? Standardized measurement repor?ng for network troubleshoo?ng ? Support for ac?ve scanning and fast ini?al link setup Dense deployments (e.g. Stadiums, train sta?ons) Outdoor deployments High interference environments (apartments and office buildings) Cellular-like Quality Robust Deployments Use Cases Air?me Efficiency Figure 2: 5G Carrier-Grade Wi-Fi (CGW) Requirements Figure 1: Growth in Public Wi-Fi locations 5G Carrier Grade Wi-Fi | 4 The Growth of Mobile Data Traffic The growth rate of mobile data traffic is two to five times greater than the growth rate of users (Figure 3). Globally, mobile data traffic will increase 13-fold from 2012 to 2017 at a compound annual growth rate of 66% (Figure 4).2 Cellular technologies may not be able to keep pace, and Wi-Fi solutions for additional cellular traffic offload will likely continue. 2 Press Release, ?Strategy Analytics: Handset Data Traffic to grow over 300% by 2017 to 21 Exabytes,? Strategy Analytics, July 3, 2013 Smartphone 20% 81% Tablet 46% 113% Laptop 11% 31% M2M 36% 89% Device Type Growth in Devices, 2012-2017 CAGR Growth in Mobile Data Traffic, 2012-2017 CAGR 66% CAGR 2012-2017Exabytes per Month 12 6 0 2012 2013 2014 2015 2016 2017 Figures in legend refer to tra?c share in 2017. Source: Cisco VNI Mobile Forecast, 2013 Other Portable Devices (0.2%) Non-smartphones (1.4%) M2M (5.1%) Tablets (11.7%) Laptops (14.0%) Smartphones (67.5%) Figure 3: Growth in Device Mobile Data Traffic Figure 4: Growth in Device Mobile Data Traffic Source: Cisco VNI Mobile Forecast, 2013 Source: Cisco VNI Mobile Forecast, 2013 5G Carrier Grade Wi-Fi | 5 Studies by companies like Cisco1 and Strategy Analytics2 predict: ? Increased mobility of users will drive the growth of mobile data traffic ? Average mobile connection speed will surpass 1 Mbps by 2014 ? Tablets will source more than 10% of global mobile data traffic by 2015 ? Monthly global mobile data traffic will peak at 21 exabytes by 2017 ? Monthly mobile tablet traffic will surpass 1 exabyte per month by 2017 Almost all subscribers with both cellular and Wi-Fi on their devices already use Wi-Fi, which accounted for 33% of all traffic from cellular devices in 2012 according to Cisco?s VNI estimates. A white paper by Senza Fill Consulting sponsored by Wi-Fi Alliance? documents how Wi-Fi traffic from mobile devices continues to provide mobile operators with valuable relief from network congestion.3 Mobile Application Trends With the significant growth of smartphones and tablets, it can be anticipated that wireless traffic will be dominated by web browsing and video transfers for these device types. These traffic types demand very high peak throughput and very high area throughput for the dense cell usage scenarios anticipated by TGax4 . It has also been noted that Wi-Fi use by consumers is different from their normal mobile use of the same smartphones. This may be a reflection of: (1) the greater speed of Wi-Fi, and (2) price sensitivity to mobile data plans that are tiered or have usage caps. Mobidia data (Figure 5) show that YouTube and downloads are far more common at home than when using the macro cellular network.5 3 Monica Paolini, ?Carrier Wi-Fi? for mobile operators,? Senza Fill Consulting, 2013 4 ?HEW Scenarios and Goals,? Qualcomm, document: IEEE 802.11-13/0542r0, May 2013. 5 J. Scott Marcus, Werner Neu , John Burns, ?Study on Impact of traffic off-loading and related technological trends on the demand for wireless broadband spectrum,? ISBN 978-92-79-30575-7, European Union, 2013. Wireless web browsing and video transfers demand very high throughput for dense usage areas. 1 Browsing Browsing Browsing 2 Facebook app YouTube Facebook app 3 Tethering Video and audio streaming Google Maps 5 Downloads iPlayer Tethering 4 YouTube Downloads E-mail Rank Cellular Wi-Fi Roaming Source: Informa/Mobidia (2012) Figure 5: Device Traffic types 5G Carrier Grade Wi-Fi | 6 IEEE Wi-Fi Standards The recently ratified Wi-Fi technology standard, IEEE 802.11ac, is foreseen as being inadequate to address the needs of 5G CGW requirements . Though 802.11ac added several enhancements to improve per user MAC throughput and optimize peak throughput, it does not fully address the requirements for a 5G CGW experience. Among the deficiencies of 802.11ac noted by IEEE members are: 6, 7, 8, 9 ? Inadequate utilization of RRM (Radio Resource Management) ? Not optimized for dense AP and STA deployments ? Lack of Inter-AP coordination ? Lack of support for multiple uplink transmissions To address these deficiencies, the WLAN standards community within IEEE has introduced a new study group, the IEEE 802.11ax Task Group (TGax), formerly the High Efficiency WLAN Study Group (HEW SG), which has been described as the next significant technology development area for 802.11. The most prominent motivation for TGax is to address the deficiencies of 802.11ac. The anticipated throughput for this technology is up to 10 Gbps, a tenfold improvement over 802.11ac. 6 ?Carrier oriented W-FI for cellular offload,? Orange, document: IEEE 802.11- 12/0910r0, July 2012 7 ?Wi-Fi for hotspot deployments and cellular offload,? Samsung, document: IEEE 802.11-12/1126r0, Sept. 2012. 8 ?Requirements on WLAN cellular offload,? NTT, document: IEEE 802.11- 12/1063r0, Sept 2012 9 ?802.11: Looking Ahead to the Future ? Part II,? Huawei, document IEEE 802.11-13/0098r0, Jan. 2013 The IEEE 802.11ax Task Group (TGax) is the next significant technology development area for IEEE 802.11 standards. Feature 802.11n(2005) 802.11ac(2008) TGax (2014) MIMO Antennas 4 8 8 Channel Bandwidth 20 and 40 MHz 20,40,80+80 MHz BW?s >160 MHz likely MAC Channel Bonding Limited func?onality Enhanced Protec?on Methods Extension to Mulitple Parallel Channels Possible MAC Channel Access Methods One AP/STA per TXOP One AP shared with Mul?ple STAs Possible mul?ple APs and STAs Mul?-User MIMO Not Supported Op?onal for downlink Poten?al likely for uplink Spa?al Streams (SS) 1-4 SS (2SS Mandatory for AP) 1-8 SS (>1 SS Op?onal) 1-8 SS (>2 SS possible) Modula?on BPSK,QPSK,16QAM, 64QAM 11n, plus 256 QAM (Op?onal) 256 QAM possibly mandatory Frequency Band 2.4GHZ, 5GHz 5GHz 2.4GHz, 5GHz Figure 6: Comparisons of recent 802.11 Specifications Source: InterDigital 5G Carrier Grade Wi-Fi | 7 5G CGW Requirements The past few evolutions of 802.11 standards have focused on improving mobile data throughput at the link layer. It is now apparent that future improvements will also require new metrics. For instance, the metric of interest for 802.11n was ?throughput? measured in bits/sec (metric). For 5G CGW, ?area throughput? should be measured in bits/sec/m2 to better reflect the performance of dense Wi-Fi deployments. Other requirements being discussed in TGax include: ? Improving Wi-Fi performance in real world deployments, both indoor and outdoor, such as for dense deployments of APs and STAs; heavily loaded BSS (Basic Service Sets); and interference from adjacent BSS ? Improving user experience and quality of service ? Reducing overheads, leading to improved spectral efficiency 5G CGW Candidate Technologies The 802.11ac specification already exploits the dimensions of frequency and space by specifying larger bandwidths and multiple antennae. This section introduces some of the new technologies envisioned for 5G CGW. Multi-User Parallel Channel Access (MU/PCA) One of the principal requirements of new amendments to 802.11 is backward compatibility with past amendments. Hence, 802.11ac is backward compatible to 802.11n and 802.11a. For example, 802.11ac has a mandatory bandwidth of 80 MHz while 802.11n and 802.11a are 40 MHz and 20 MHz wide respectively. Backward compatibility is maintained with 802.11ac by allowing an 80 MHz-capable AP to transmit only to one narrower band STA at a time on a primary channel. However, this inevitably leads to underutilization of frequency resources as shown in Figure 7. Figure 7: InefficientFrequency Resource Utlilization Data ACK Channel 1 Channel 2 Channel 3 Channel 4 Idle frequency bands Data ACK Data ACK STA1 STA2 AP STA4 STA3 Source: InterDigital 5G Carrier Grade Wi-Fi | 8 Multi-User Parallel Channel Access (MU/PCA) schemes that are backward compatible with the existing CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) but also allow multiple users to transmit simultaneously in parallel frequency sub-channels can significantly improve throughput. Figure 8 shows the throughput improvement that can be achieved when an 80 MHz capable AP transmits to four 20 MHz STA?s simultaneously for different packet sizes. Significant throughput gains of 250% - 300% have been shown to be possible using such schemes .10 Fractional CSMA (FCSMA) and Transmit Power Control (TPC) One of the deployment scenarios of interest to 5G CGW is dense deployments of APs. This inevitably leads to Overlapping Basic Service Sets (OBSSs). When available, adjacent APs in OBSSs may choose different frequency bands of operation, but in some cases this may not be possible. When multiple OBSSs use the same frequency bands, interference becomes a problem especially for STAs on the edge of coverage. The increased interference results in a reduction in the network throughput as seen at the Media Access Control (MAC) layer and an increase in energy expenditure. The effect of transmission in OBSSs is illustrated in Figure 9 in which AP1 and AP2 independently transmit data to STAs in their BSSs simultaneously. The transmission from AP1 to STA1, BSS1 (shown in brown) may fail due to the transmission from AP2 to STA3, BSS2 (shown in blue). Multi-User Parallel Channel Access (MU/PCA) can improve Wi-Fi uplink throughput by 250 to 300%. Th ro ug hp ut (M bp s) 500 500+1500 1500 MU/PCA CSMARTS/CTS CSMA w/o RTS/CTS Packet size (Bytes) DL MU/PCA vs. CSMA (20MHz) 54 9 13 76 16 21 114 22 27 120 100 80 60 40 20 0 Figure 8: Efficient use of parallel frequency channels can provide 2x to 3x throughput improvement 10 H. Lou, X. Wang, J. Fang, M. Ghosh, G. Zhang and R. L. Olesen, ?Multi- User Parallel Channel Access for High Efficiency Carrier Grade Wireless LANs,? InterDigital, ICC 2014 Source: InterDigital 5G Carrier Grade Wi-Fi | 9 With appropriate Transmit Power Control (TPC) mechanisms and inter-BSS coordination, it is possible for the two APs to transmit simultaneously with few or no collisions. One such mechanism is a Fractional CSMA/CA scheme in which only a fraction of the total STAs are permitted to access the channel at a specific time. The access duration is coordinated between multiple BSSs to limit the amount of interference experienced . TPC is incorporated to ensure that the interference resulting from the coordinated transmissions is limited. The technique implicitly reduces the coverage of a subset of the BSSs in the network, reducing the amount of overlap and hence improving the system performance. Figure 10 shows the downlink performance improvement that may be achieved using these methods. Similar improvements of approximately 80% to 100% in throughput are observed on the uplink as well.11 Figure 9: Overlapping BSS transmissions Fractional CSMA reduces the overlap of Basic Service Sets, improving Wi-Fi performance. Pe rc en ta ge G ai n (E ne rg y N or m al ize d Th ro ug hp ut ) Downlink: Overlapping BSS, inter-AP distance of 800m 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Unfiltered TPC- Packet- FCSMA Off Filtered TPC- Packet- FCSMA Off Unfiltered TPC- Packet- FCSMA On Filtered TPC- Packet- FCSMA On Figure 10: Downlink throughput gains with FCSMA and TPC Source: InterDigital Source: InterDigital 5G Carrier Grade Wi-Fi | 10 Uplink Multi-User MIMO (UL MU-MIMO) The 802.11ac specification introduced for the first time in 802.11 the concept of transmitting to multiple users at the same time within the CSMA/CA MAC using Multi-User MIMO (MU-MIMO). However, this was only restricted to one-way transmissions ? i.e., multiple transmissions from a single AP to multiple STAs or downlink MU-MIMO. This allows increased throughput on the downlink. However, the uplink throughput does not increase. With UL MU-MIMO, multiple STAs (with fewer antennae) can simultaneously transmit to an AP with a larger number of antennae. For example, four single-antenna STAs can transmit to an AP equipped with four antennae. With increasing volumes of user-generated data being uploaded to social networking sites, increasing the uplink throughput in this way would significantly improve the user experience. Additionally, most of the complexity would reside at the AP. 12 Some of the technical challenges of implementing UL MU-MIMO include: ? Synchronizing uplink users in frequency and time to enable coherent decoding at the AP ? Grouping of users such that the capacity is maximized ? Power control to ensure proper AGC operation at the AP These challenges can be overcome with appropriate system designs and algorithms, such as those currently being developed and tested by InterDigital . Next Steps: Collaboration with Industry and University Partners InterDigital has brought to bear years of experience with Wi-Fi technology to develop innovative solutions that can achieve four to six times the capacity of IEEE 802.11ac with cellular-like quality. Our 5G CGW technology has been widely published in journals and discussed at industry events. As 5G CGW moves towards reality, InterDigital looks forward to collaborating with industry and university partners to transition the technology from concepts to reference platforms, and then to deployed products. 11 O. Oteri, P. Xia, F. LaSita and R. L. Olesen, ?Advanced Power Control Techniques for Interference Mitigation in Dense 802.11 Networks,? InterDigital, Invited Paper, Global Wireless Summit, June 2013 . 5G Carrier Grade Wi-Fi | 11 Acronyms 5G: Fifth Generation AGC: Automatic Gain Control AP: Access Point BSS: Basic Service Set CSMA: Carrier Sense Multiple Access CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance CGW: Carrier-Grade Wi-Fi FCSMA: Fractional Carrier Sense Multiple Access HEW SG: IEEE 802.11 High Efficiency WLAN Study Group MAC: Media Access Control (address) MIMO: Multiple Input and Multiple Output MU-MIMO: Multi-User MIMO MU/PCA: Multi-User Parallel Channel Access OBSS: Overlapping Basic Service Sets PAR: Project Authorization Request RRM: Radio Resource Management STA: Station TPC: Transmit Power Control UL MU-MIMO: Uplink Multi-User MIMO VNI: (Cisco) Visual Networking Index Further Reading H. Lou, X. Wang, J. Fang, M. Ghosh, G. Zhang and R. L. Olesen, ?Multi- User Parallel Channel Access for High Efficiency Carrier Grade Wireless LANs,? InterDigital, ICC 2014. O. Oteri, P. Xia, F. LaSita and R. L. Olesen, ?Advanced Power Control Techniques for Interference Mitigation in Dense 802.11 Networks,? InterDigital, Invited Paper, Global Wireless Summit, June 2013. ?Uplink intensive usage models,? Qualcomm, 802.11ac, document IEEE 802.11-09/0849r1, July 2009. H. Lou, M. Ghosh, P. Xia and R. L. Olesen, ?A comparison of implicit and explicit channel feedback methods for MU-MIMO WLAN systems,? InterDigital, PIMRC 2013. M. Ghosh, ?A comparison of normalizations for ZF precoded MU-MIMO systems in multipath fading channels,? InterDigital, IEEE Wireless Communication Letters, 2013. P. Xia, M. Ghosh, H. Lou and R. L. Olesen, ?Improved transmit beamforming for WLAN systems,? IEEE WCNC 2013, pp. 3500 - 3505, April 2013 . About InterDigital? InterDigital develops technologies that are at the core of mobile devices, networks, and services worldwide. We solve many of the industry?s most critical and complex technical challenges, inventing solutions for more efficient broadband networks and a richer multimedia experience years ahead of market deployment. InterDigital has licenses and strategic relationships with many of the world?s leading technology companies. Founded in 1972, InterDigital is listed on NASDAQ and is included in the S&P MidCap 400? index. InterDigital is a registered trademark of InterDigital, Inc . WP_201406_004 For more information, contact solutions@interdigital.com Published July, 2014