As operators and equipment providers work towards the definition and deployment of next-generation networks, it is becoming clear that the next evolutionary step for cellular architectures requires a fundamental change in approach: a whole new dimension is being added to wireless technology – that of “topology”. The brunt of network traffic can no longer be carried by the traditional macrocell basestation arrangement, but must travel via fine-grained networks of much smaller cells.
Market and technical data indicates that 4G technologies such as LTE (long-term evolution) will be of most use in metropolitan areas and enterprise hotspots, delivering improved coverage and enhanced capacity for operators – a strong deployment motivation. Such usage models will only serve to escalate many of the challenges facing the industry and introduce a new raft of technical and financial questions that need answering.
Approximately 60% of mobile usage already takes place indoors, yet providing in-building coverage is a technical problem at the gigahertz frequencies used for Wimax and LTE. This is only set to get worse as the mobile continues to replace the home phone. Research indicates that, as “all you can eat” data packages become commonplace, this number is likely to reach 75% by 2011.
As transmission frequency increases, in-building penetration degrades. The additional attenuation reduces throughput for those users indoors, but there is another effect too: if the traditional macrocell allocates more power to reach the indoor user, this increases the interference for other users. Such realities inevitably have a quantifiable, negative impact on cell capacity, making it impossible to deliver 10 times the performance of 3G that is a fundamental requirement of the 4G vision.
Furthermore, the large cell approach is fundamentally less able to provide the benefits for which LTE was intended. As Cooper’s Law identifies, the best way to increase traffic density is via smaller cell sizes. A macrocell gets hit twice in this respect – it has poorer total throughput due to RF conditions and it has to spread that throughput over a much wider area.
Most operators considering the roll-out of LTE already have widespread HSPA networks. If terminal devices are going to be multimode (LTE and HSPA and GSM, for example), there is little point in deploying LTE everywhere and ensuring ubiquitous coverage, since the user experience may be no better than that provided by HSPA (or could be worse). The capital expenditure of a small cell approach need not be prohibitive. Indeed, substantial savings will be available on the back of the technological innovations that are driving down the bill of materials costs for residential femtocells.
A small cell approach also has cost implications for operating expenditure. These networks need to incorporate self-optimising technology to eliminate manual configuration during deployment and throughout the life of the equipment. These self-optimising networks (SONs) will, for instance, dynamically optimise radio network performance in use and provide intelligent backhaul capabilities. Operators are already recognising these requirements and mandating the provision of SONs; the emerging residential femtocell in WCDMA is proving this capability now.
This network architecture change will produce corresponding changes throughout the infrastructure value chain. The network equipment industry will move towards a consumer market approach – in a manner similar to the use of “commercial off-the-shelf” (COTS) technologies in the military equipment market, infrastructure manufacturers can borrow from femtocell innovations to benefit from consumer electronics economics. This will place an onus on IC suppliers to offer unprecedented levels of systems-level expertise and support.
The traditional macrocell approach will flounder at the next stage of network evolution: they are too expensive a solution and do not deliver the required results.
4G technologies excel when providing extra coverage/capacity in targeted metropolitan hotspots and in-building areas. The capital expenditure and operating expenditure of deploying like this are enabled by exploiting consumer electronics component technologies and the emergence of SON technologies which are already in use in the residential femtocell arena. To compete and survive in the 4G market, infrastructure providers will need to adopt a more consumer-orientated approach than they have historically.
Dr Doug Pulley is co-founder and CTO of picoChip