OFDMA Femtocells

There could be upto 70 million Femtocells by 2012 in world. If this happens the big problem would be the interfacerence between Macro and Femtocells and also between Femtos. OFDMA (used in LTE and WiMAX both) Femtocells can handle the interference better than CDMA Femtocells duo to is Intracell interference avoiding properties and robustness to multipath.

Interfere analysis will definitely play an important part in the rollouts. If not properly manged, could result in dead zones within Macro. Power control Algorithms and Radio Resource Management strategy will help but effective Spectrum allocation technique is needed as well. The diagram above shows different approaches for subchannel allocation in OFDMA femtocells.



The Femtocells would need to be self-configurable and self-optimising. Self-configuration comes into picture when the Femto is switched on. Once the parameters are adjusted then Self-Optimisation tries to optimise these defaults into something better and more suited to the current environment. Sensing of the environment plays an important part. This diagram above shows different approaches being used by different Femtocells. The cheapest approach would of course be the measurement report approach where the phone is made to report the environment. The only problem being that whichever phone was used (automatically selected) will have considerable amount of its battery power used up.

参考：3g and 4g wireless blog

Femtocells for LTE

As you may have heard that in UK, Vodafone rolled out Femtocells which have now been branded as 'Sure Signal'and the device now costs less than half the initial price. At the same time, some small players are getting more interested in the small cells for LTE.

The femot players are looking ahead to LTE, where there are many indications from operators that tiny cells will play a big part in the strategy. The devices will be used from day one by some carriers - to offload data from the macrocell or to provide indoor coverage in high frequencies like 2.6GHz. They could also add capacity to deployments in low frequencies like 700MHz and even be used as a starting point for greeen field providers, which could then add macro networks later, explained Simon Saunders, chair of the Femto Forum.

Continuous Computing has been eyeing the femto market for serveral years from its heartlands in protocol stacks, core networking and traffic shaping. At MWC, it worked wiht picoChip and Cavium Networks to show the first complete LTE femtocell reference design. Available immediately, this includes the LTE modem, RF and packet processors, protocol software, intelligent router functionality and a complete Evolved Packet Core (EPC) simulator.

The demand for LTE femtocells is unquestionable. WE are already seeing operors asking for small cell access points to start testing in the second half of this year. Femtocells represent the key to avoiding the difficulties surrounding the first 3G deployments where roll-outs cost too much. took too long and did not meet user expectations.

参考：http://www.theregister.co.uk/2010/02/18/mwc_femtocell_spotlight/

LTE Femtocell

Many people in our industry are now of the opinion that the best way forward with LTE is to roll them out as Femtocells and then when more and more people start using them, then start deploying LTE Microcells/Marcocells

Approximately 60% of mobile usage already takes place indoors, yer providing in-building coverage is a technical problem at the giahertz frequenies 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 of is like to reache 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-optimisting tehcnology to eliminated manual configuration during deploment and throughput the life of te equipment. These self-optimising networks(SONs) can dynamically optimise radio network performance in use and provide intelligent hackhaul capabilityies. Operators are already recoginsing these requirements and mandting the provision of SONs: the emerging residential femtocell in WCDMA is proving this capability now.

This network architecture change will produce corresponding changes throughput the infrastructure value chain. The network equipment industry will move towards a consumer market approach - in a manner similar to the use of "commerical off-the-shelf" (COTS) tehconogies in the military equipment market, infrastructue manufacturess can borrow from femtocell innovations to benfit from consumer electronics economics. This will place an onus on IC sumppliers to offer unprecedented levels of system-level expertise and support.

The tradistional marcocell approach will flounder at the next stage of network evolution: they are too expensive a solution and do not deliver the required results. It is time to femtocells for LTE.



参考：3G and 4G wireless Blog
http://gigaom.com/2008/09/15/4g-forget-cell-towers-bring-on-the-femtocells/
http://www.electronicsweekly.com/Articles/2008/09/15/44506/the-macrocell-is-dead-long-live-the-network.htm

LTE Femtocell in NTT DoCoMo

NTT DoCoMo's managing director, Yoshiyuki Yasuda, said that they plan to roll out LTE Femtocells next year manly to fill the coverage gaps in the LTE Network they will be rolling out later this year.

Which vendors can serve up the LTE femtos in time? NEC Corp., which is already one of DoCoMo's LTE vendors, has revealed plans for an LTE home base station that will be available for friendly user trials at the end of 2011, and commercial product is expected in 2012.

Other vendors that are involved in Fujitsu Ltd., Ericsson AB, and Nokia Siemens Networks, and Stoke Inc.

DoCoMo's Yasuda said that when the carrier wants to deploy LTE femtos in the 2011-2012 timeframe, it will have deployed 1,500 LTE macrocell base stations during 2010 and 2001. By 2013, it plans to cover 30% of the population with LTE. By 2014, DoCoMo plans to cover 70% of the population with 15,000 LTE base stations.