Are LTE and mobile WiMAX really 4G networks? A look at ITU-R IMT Advanced attributes

There have been several recent articles comparing and contrasting LTE vs. mobile WiMAX as potential 4G network technologies. Indeed, SPRINT and Clearwire have been marketing their WiMAX offering as a 4G service. But is it really 4G? Is LTE a 4G technology? What about ultra-wideband?

It turns out that no broadband wireless technology can legitimately claim to be 4G, because the ITU has not completed its 4G specifications yet (4G is known as IMT Advanced in the ITU-R). Hence, there is no benchmark document(s) for which to evaluate any of the proposed 4G technologies. Several important ITU documents and presentations are listed in the References at the bottom of this article.

What are the attributes of 4G?

The ITU has stated that 4G will be a "completely new, fully IP-based integrated system of systems and network of networks- achieved after convergence of wired and wireless networks." This is in sharp contrast to current 3G networks, which are circuit-switched based, with an overlay of data carrying capabilities (EVDO for CDMA and HSDPA for GSM). 4G networks will be entirely IP packet switched. Mobile voice will be carried as a stream of IP packets–VoIP over the equivalent MAC sub-layer.

According to the ITU, 4G networks will be capable of providing 100 Mbps and 1 Gbps downstream rates, in outdoor (mobile) and indoor (fixed access) environments, respectively. 4G networks will have end-to-end QoS and high security, offer any kind of services at any time as per user requirements, anywhere with seamless interoperability, always on, affordable cost, one billing and fully personalized.

Here are the key features of 4G/IMT-Advanced (as per ITU-R document: BACKGROUND ON IMT-ADVANCED, 7 March 2008- see References below):

• a high degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner;
• compatibility of services within IMT and with fixed networks;
• capability of interworking with other radio access systems;
• high quality mobile services;
• user equipment suitable for worldwide use;
• user-friendly applications, services and equipment;
• worldwide roaming capability; and,
• enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility were established as targets for research).
• These features enable IMT-Advanced to address evolving user needs, which implies a network that will evolve and change over time.

The 4G Radio technologies will include:

• Orthogonal Frequency-Division Multiple Access (OFDMA)- a highly efficient multi-carrier modulation scheme, and
• Multiple Input Multiple Output (MIMO)- a multi-antenna system that minimizes data errors and optimizes speed.

How do LTE and mobile WiMAX stack up against the 4G/IMT-Advanced Objectives?

Both LTE and WiMAX are based on OFDMA and MIMO technologies and both are all IP networks with QOS and (some) security. 3GPP’s initial LTE specification, due in March 2009, is that organization’s choice for a 4G network. As noted in an earlier post today, IEEE 802.16 TG m is chartered with ammending the IEEE 802.16 WirelessMAN-OFDMA specification to meet IMT-Advanced requirements, while offering continuing support for legacy WirelessMAN-OFDMA equipment. This will provide an UPGRADE path for existing mobile WiMAX networks based on IEEE 802.16-2005 to a 4G-like network.

But it remains to be seen if either of these networks will qualify as 4G/ IMT-Advanced networks when they are initially rolled out. It will take a long time to validate their attributes and operational performance against the numerous IMT Advanced requirements. Let’s not take all the hype too seriously at this time.