Expert Opinion

Expert Opinion
Short LTE articles and opinions by our team of Subject Matter Experts (SMEs)


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Coming to a Theater near You…

If you came here in search of an action-packed thriller starring LTE and WiMAX, you are at the right place!  In this movie flick, the stakes are high…the winner will dominate the 4G cellular market.  LTE is Long term Employment, Oh…Long Term Evolution, and WiMAX stands for Worldwide Interoperability for Microwave Access.  LTE and WiMAX are two major 4G cellular technologies.  The LTE vs. WiMAX debate is reminiscent of the erstwhile GSM vs. CDMA battle.  We'll compare LTE and WiMAX from the perspectives of air interface features, network architecture, and industry trends.  In general, they share more similarities than differences.  WiMAX in this article refers to IEEE 802.16e-2005-based mobile WiMAX.

Air Interface Features.

Both LTE and WiMAX aim for superior packet data performance with the peak user data rates in excess of 100 Mbps (e.g., 300 Mbps) and latency less than 10 ms.  Achieving such data rates is no small task, and, technologies such as OFDMA and advanced antenna systems are called upon by LTE and WiMAX.  While WiMAX uses scalable OFDMA for both downlink and uplink, LTE uses scalable OFDMA in the downlink and a variation of OFDMA called SC-FDMA (Single Carrier- Frequency Division Multiple Access) in the uplink.

The use of SC-FDMA results in reduced PAPR (peak-to-average power ratio) for the mobile device at the expense of increased complexity in both the device and the base station.  In practice, such PAPR reduction could be reflected in a somewhat larger cell radius or better cell-edge performance in the uplink.  The typical subcarrier spacing is 10.94 kHz in WiMAX and 15 kHz in LTE.  Such spacing makes the job of the WiMAX receiver a little easier due to flat fading and allows LTE to support faster moving vehicles due to additional resistance to Doppler shift.  While STC (Space Time Coding) is a more common transmit diversity for WiMAX, a variation of STC called SFBC (Space Frequency Block Coding) is used in LTE.

Both WiMAX and LTE support MIMO (Multiple Input and Multiple Output) and SDMA (Space/Spatial Division Multiple Access) in the downlink and SDMA in the uplink.  SDMA is referred to as MU (Multi User)-MIMO in LTE and Collaborative Spatial Multiplexing in WiMAX.  In terms of performance, peak user data rates are approximately 75 Mbps and 63 Mbps in the downlink of LTE and WiMAX, respectively, and 37.5 Mbps and 28.8 Mbps and in the uplink of LTE and WiMAX, respectively.  These performance estimates assume (10 MHz x 10 MHz) FDD and the use of 2x2 MIMO in the downlink.

The performance gap between LTE and WiMAX from the perspectives of average sector throughput and user perceived throughput would be narrower than that for peak performance.  The VoIP capacity of LTE can be expected to be somewhat higher than WiMAX due to more efficient resource allocation techniques.  While both technologies will eventually support TDD and FDD, early WiMAX deployments use TDD and initial LTE deployments are expected to use FDD.

Network Architecture.

The LTE radio network consists of eNode Bs, while the WiMAX radio network consists of BSs and ASN-GWs (Access Services Network- Gateway).  The WiMAX core network uses typical IP network nodes such as AAA Server, Home Agent, DHCP Server, and DNS Server and can connect to a Services Network such as IMS.  LTE defines a comprehensive core network called EPC (Evolved Packet Core). This includes special entities such as MME (Mobility Management Entity), HSS (Home Subscriber System), S-GW (Serving Gateway), PCRF (Policy & Charging Rules Function), and PDN-GW (Packet Data Network Gateway) in addition to the nodes mentioned for WiMAX.  It is conceivable that EPC may be used by a WiMAX radio network.  EPC can also connect to IMS.

Industry Trends.

WiMAX enjoys a broad ecosystem with competition among numerous vendors, many of them small companies, potentially resulting in a lower cost BS and MS.  Most big manufacturers have WiMAX offerings, Motorola, Samsung, Nokia, Alcatel-Lucent, Nortel, Intel, and Cisco.  Intel and Cisco are new entrants to the mobile cellular world.  Notably absent from the WiMAX list are Qualcomm and Ericsson.  LTE has backing from traditional cellular companies including major 3G operators covering more than 90% of the cellular market.

LTE is offered by the WiMAX companies mentioned earlier except Cisco and Intel.  Assuming (!) that some 1xEV-DO and UMTS systems see LTE overlays, there could be huge economies of scale benefit due to the large number of subscribers, leading to low cost user devices.  The cost per eNode B may be somewhat higher than a WiMAX BS due to relatively less intense competition as the typical LTE vendors are likely to be major vendors who may not face serious threats from small companies.  In summary,  Both LTE and WiMAX have a solid backing from industry heavyweights, which provides adequate ammunition  in the fight for dominance!
Conclusion of the Movie…

Looking into the crystal ball, it appears that both systems would co-exist, sometimes as complementary technologies but more often as adversaries.  Furthermore, the technologies will play cat-and-mouse, learning from each other's shortcomings to improve their future revisions.  For example, WiMAX would aim to close the performance gap with LTE using 802.16m.  At this time, LTE seems to have a performance advantage and WiMAX seems to have time-to-market advantage.  Stay tuned for a sequel as the battle for 4G rages on…

  • Nice Review Nishith. Thanks !!!

  • Dr. Nishith,

    Can you please provide 10 MHz WiMAX vs 10 MHz LTE TDD? In WiMAX TDD, with 75/25 DL and UL ratio, 5 Map symbols,  you can get around 43Mbps in MIMO B DL. With similar configuration, what throughput could be achieved with LTE?