Technology battles are commonplace in the telecom sector. The GSM versus CDMA battle, which divided the wireless world into opposing camps, was one of the most contentious ones in the wireless infrastructure place. Another technology debate in the sector was the choice between internet protocol (IP) and asynchronous transfer mode. The latest tug of war is being witnessed in the broadband market with Wi-Max pitted against long term evolution time division duplexing (LTE TDD).
The scales seem to be tilting in favour of LTE, even though the technology is yet to see mass deployment. Wi-Max?s pockets of resistance include fixed applications in emerging markets, rural markets in developed countries, niche applications in vertical markets such as electric smart grids, etc.
With ultra-mobile broadband out of the reckoning for 4G, LTE and Wi-Max remain the only viable future options. This has created a ground for opposition between the proponents of these technologies. The main issue is that network evolutions and ultimately, the underlying technologies are almost always driven by competition rather than real demand.
From a technical standpoint, LTE and Wi-Max are very similar with IP and orthogonal frequency division multiplexing access (OFDMA) as core components. Wi-Max802.16e with migration to 802.16m shares similar performance capabilities with LTE as these technologies exploit similar wireless and IP design techniques to approach maximum spectral efficiencies (defined by Shannon?s Law [approximately 6 bits per Hz]). While 802.16e operators can deliver speeds of over 3.5 bits per Hz (35 Mbps per sector for a 10 MHz channel), 802.16m and LTE will increase this to over 5.0 bits per Hz (greater than 100 Mbps per sector for a 20 MHz channel).
There are, however, some major differences. A key distinction is the fact that Wi-Max is based on IEEE while LTE is based on 3GPP. IEEE has a proven history of being more supportive of open standards than 3GPP. Another important difference between the two technologies is the deployment requirements. While Wi-Max requires a new network to be built, LTE is an evolution of existing WCDMA/HSPA networks, and, therefore, has the footprint advantage of close to 80 per cent of global subscribers.
Wi-Max
Wi-Max serves several functions in wireless connectivity, but is largely meant to provide ?last mile? broadband connectivity to homes and businesses. The technology, which does not require line-of-sight, uses transmitters like mobile towers to carry signals. It is particularly useful and cost effective for rural homes and other locations where laying a traditional hardwire is difficult or expensive.
Currently, mobile Wi-Max (IEEE 802.16e) is being widely used while the fixed version (802.16d) of the technology is restricted to niche segments. The fixed version is primarily being used for broadband solutions for homes and can be used for backhauling remote offices or mobile stations. Mobile Wi-Max is a TDD (and frequency division duplexing [FDD]) technology. Both the uplink and the downlink share the same bandwidth, which is divided into time slots. As a result, this technology does not need a pair of frequency bands. In addition, Wi-Max is also spectrally flexible. It operates in a number of different carriers ? 2.3 GHz, 2.5 GHz, 3.3 GHz, 3.5 GHz, and 5 GHz and above.
The physical layer features OFDMA in both the downlink and uplink paths with TDD access mode being standard in the Wi-Max 1.0 system profile. FDD was later added in Wi-Max 1.5 but the ecosystem does not fully support this feature yet. Multiple antenna techniques are supported with space time block codes (Alamouti scheme) and spatial multiplexing is supported with adaptive switching between the two modes.
The technology provides each user a constant allotment of broadband access. An algorithm is built into the Wi-Max technology, which establishes a limit to the number of users accessing each Wi-Max point. When a Wi-Max tower is nearing its maximum broadband capacity, it automatically redirects additional users to another access point.
Flexible bandwidth allocation and multiple built-in types of quality-of-service support in the Wi-Max network allow the provision of high speed internet access, VOIP and video calls, multimedia chats, mobile entertainment, etc. In addition, the Wi-Max connection can be used to deliver content to multimedia gadgets.
Going forward, the standard?s 802.16m version, which is being developed over the past five years, is expected to be finalised in March 2011 and deployed in end-2011 or early 2012. The Wi-Max mobile version (802.16m) can be used as a replacement for GSM and CDMA technologies. The technology operates at a frequency of 20 MHz, twice that of the existing 802.16e, thereby enabling signals to carry double the amount of network traffic, which has increased with the use of iPhones and other modern devices.
Samsung Electronics has already demonstrated the Wi-Max 802.16m version, which transmits data at a speed of up to 330 Mbps. This technology is backward compatible with the existing network infrastructure.
LTE TDD
While Wi-Max 802.16e has a two-year headstart over LTE, the latter offers more flexibility as spectrum can be allocated from the 1.3 MHz to 20 MHz bands, allowing LTE to be added in bands with existing technologies. LTE TDD is also undergoing standardisation due to market needs, especially in China in connection with TD-SCDMA. All 3GPP operators already have spectrum that can be used for LTE. In the case of both technologies (LTE TDD and TD-SCDMA), the amount of available spectrum and channelisation will weigh heavily on the quality and bandwidth that they are able to offer customers.
LTE TDD shares its technical basis with LTE FDD and in fact, differs little from it, except for the duplexing scheme. This means that a large part of the global investment in the development of LTE will also be available for the LTE TDD variant.
LTE TDD uses OFDMA for downlink and single carrier FDMA for uplink (exactly like LTE FDD) and applies the same modulation schemes up to 64QAM. These are robust multiple-access schemes that ensure optimal radio conditions for high data rates and many concurrent users per cell.
In particular, LTE TDD (and LTE FDD) excels at being robust against multipath fading (damage to the radio signal due to multiple reflections) and is highly scalable. Strong resistance to multipath fading means that LTE TDD is inherently capable of delivering a high useful data rate per unit bandwidth, thereby offering high spectral efficiency.
LTE TDD uses a single continuous frequency band for both uplink and downlink data streams by splitting the signal in time. For this to work, a small time delay ? a guard frame ? is introduced to separate the send and receive periods of the data stream. This ensures that the device and base station have sufficient time to switch between ?transmit? and ?receive? modes.
The common technical basis for LTE TDD and LTE FDD will also allow service providers to operate combined networks, or even share network infrastructure and reduce capex and opex. A key feature of the technology is its asymmetry. The uplink and downlink data rates can be varied dynamically, albeit at a relatively slow rate, to meet different requirements. The downlink rate can be increased to nine times the uplink rate by splitting the time durations correspondingly. This is useful for broadcast or browsing applications that are naturally asymmetrical.
On the performance front, the difference between theoretical peak rates and real data rates is expected to be significant, as LTE TDD is more susceptible to in-band interference degradation than LTE FDD. The technology?s performance will depend on a number of factors including cell loading.
Although LTE TDD is lesser known than LTE FDD, the global vendor and operator community is well on its way to developing fully operational LTE TDD solutions and services. China Mobile?s commitment to LTE TDD is an important factor contributing to the overall development of the ecosystem and economies of scale for the technology, since the operator has a huge potential LTE TDD subscriber base. This technology is rapidly emerging as the preferred choice for mobile broadband in unpaired bands.
Net, net, even as the battle between Wi-Max and LTE continues unabated, both technologies are well positioned to drive the global evolution towards pervasive wireless broadband communication.
