In two previous blog entries I focused on the limited uplink power of mobile stations and how WiMAX, UMTS/HSDPA and LTE overcome this hurdle by allowing several mobiles to transmit simultaneously. In the future, however, limited transmission power might not be the only limitation.
WiMAX and LTE will probably both use a technology called MIMO (Multiple Input / Multiple Output) which makes use of multiple antennas at both the transmitter and the receiver to transmit independent data streams on the same frequency via different directions. Especially small hand held devices, however, might not be equipped with several antennas due to their small size or due to the additional cost incurred. Thus, they can not make use of MIMO. This reduces both their own speed as well as the overall speed of the network.
The solution to this problem is called "uplink collaborative MIMO" or multi user MIMO (MU-MIMO). Here, the network can instruct, for example, two mobiles to transmit simultaneously, each on an independent MIMO path. Even though both signals are sent on the same frequency, a MIMO capable base station will still be able to pick up the signals independently from each other if the main energy of each signal arrives from a different direction. This in effect creates a MIMO channel, just that the two or more antennas do not belong to one terminal but to several. Interesting approach!
From what I can read in the press, only Nortel has so far picked up on this and has stated that it will implement collaborative MIMO in the uplink direction for both WiMAX (here and here) and LTE (here).
5 thoughts on “Collaborative MIMO for WiMAX and LTE”
I think you should have mentioned the key differentiating factor betwee DL and UL MIMO. UL collaborative MIMO does not increase a user’s peak data rate. It only increases the number of users that can be supported by the BS since you reuse tones.
Gr8 blog, I must say. Always enjoy reading your articles. 🙂
UL collaborative MIMO in a mandatory feature in wave-2 compliant wimax terminals. so it is not a question whether nortel or any will support it – it is mandatory. (IO-MIMO on BS)
Nokia Siemens Networks now also talks about the subject: http://www.3g.co.uk/PR/May2007/4629.htm
MIMO-AAS, CO-MIMO, MU-MIMO are actively being added to both LTE as well as WiMAX, often by the same companies. This is also reflected by an rapid increase in the numbers of patents that have been filed internationally in these segments of technology.
I see the pace of IPR has picked up to a torrent and the time between filing for patents and proposals to standards groups can be almost simultaneous.
Also interesting is activity in a group of technologies I summarize as ‘smart distributed wireless BB networking’ or simply SDWN. This is an arbitrary segmentation of classes of technology that can be used in NG networks that leverage MIMO-AAS methods to build more easily self-configuring, adaptive self back-haul, upon link technologies, sub-channel measurement and estimation, QoS, etc.
SDWN is supported within the frameworks of the standards but also can go outside the standards into proprietary enhancements to individual or co-developments or licensing partnerships. We are seeing that at several levels as competitive differentiation is sought. Arraycomm, Navini/Cisco in partnerships to implement MIMO-AAS and individual IC companies that claim higher performance implementations or higher order MIMO beyond core requirements. I suspect we may see similar collaboration on MU-MIMO/CO-MIMO, virtual base stations/remote stations and other developments.
Some of this is speculative but because of significant link and network performance gains and potential to reduce site and deployment costs, I expect to see relatively very fast development and commercial offerings.
The commercialization of much of these methods has been a ‘harry brained figment of my imagination’ for several years but now is coming to fruiting. This is seen in enabling IC developments that offer network processing, MIMO-AAS capability and ability for further enhancements via software including CO-MIMO. And it is an active part of system developments increasingly showing promising results in trials beyond the lab.
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