(a) A scheme for reuse of almost 1. Reuse of 1 means that you can reuse the same frequency in every cell. Reuse of 1/3 means that you can reuse the same frequency in one out of 3 cells. This is what "Reuse" means to a cellular system.
- the big mistake in GSM systems is for reuse they have to solve a problem like the 4-color problem, and reuse 1/3rd is about the limit. This means that in many cases you need 3 bands to provide adequate service in a GSM system. If you do not use separate frequencies, then one user on the edge of a cell in a narrow band will heavily interfere or destroy the signal from another user nearby on the same frequency in the neighboring cell.
Qualcomm solved this problem with pseudorandom noise (PN) codes which averages interference between these edge users, and allows Qualcomm systems to use 1 frequency throughout the network. The net benefit is about 1/3rd less frequency is needed for a given deployment, saving money in spectrum auctions, or allowing 3x more capacity to be squeezed from a unit chunk of spectrum, making 3G multi-megabit performance realistic.
(b) A technique to improve the performance and link budget of edge users during handoff.
A worst-case situation that you always fear in a cellular design is when all users go out to the edge of the cell, how can the base station, which is on a finite power budget, and the handset, which is facing noise from other base stations, get good service so that calls are not dropped during handoff? Soft handoff elegantly solves both problems at once, it allows up to 2x the power to be delivered to the handset, and at the same time, decreases noise because both cells are synchronized and targeting the same handset at the same time, rather than targeting different handsets and creating interference / hurting handset performance. This patent is one that really matters at lot.
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And no, to the best of my knowledge, Flarion and 802.16 do not have solutions for both of these problems, and this may be one of the reasons why both began touting their system as a fixed wireless broadband system rather than as a mobile system with good handoff performance. |
