Femtocell CDMA and WiMAX, how’s the GPS synchronization?

Salam..

As mentioned before in my last post, Femtocell is applicable to all standards, including GSM, CDMA2000, TD-SCDMA and WiMAX solutions. So how’s the synchronization issue in femtocell CDMA and OFDM based, since it is installed for indoor building? Thanks for google technology, for giving me much information to write this post.

We know that 3G Technology commonly based on CDMA and OFDM, i.e., CDMA20001x EVDO/EVDV, WCDMA and WiMAX. CDMA is a synchronized technology, which needs GPS to perform accurate signal aquisition and snycrhonization. Femtocell is applicable for those 3G technologies to enable indoor user access data service such as internet, mobile tv, video streaming etc. But, if we install femtocell in our building, how about the snycrhonization? since GPS signal couldn’t penetrate favorably in indoor environment.

why GPS synchronization?

It deals with location, frequency and Timing Syncrhonization.

Location determination : is used for Emergency caller identification, Cellular Operating License verification and Control of Customer Usage.
Frequency stability : maintain spectrum aquracy with neighboring cell. (macro cell incase femtocell)
Timing synchronization : CDMA and WiMAX must be synchronzied to within 1-3 micro seconds to maintain call handoff and avoid interference.

Rosum, has its own solution to contend this matter. They called this product femtosynch. Well let’s dive on to this technology deeper. Below a picture which explain briefly the TV-GPS technology.

Building penetration attenuation is a critical point in GPS technology. To compare RF attenuation, I filch this table from Rosum’s paper.

How femtosynch works?

The picture below will guide us to understand how this TV-GPS technology works.

As I read on Rosum’s site, there are several TV’s advantages to conduct GPS functionality i.e,.

Power
Rosum TV-GPS enjoys a substantial power advantage over GPS signals. Terrestrial TV broadcast signals are typically 1 megawatt effective radiated power (ERP), compared to 500 watts ERP for GPS satellite signals. In typical metropolitan environments, TV towers are tens of miles from the user device to be positioned. The result is that the synch codes in the TV signal (which Rosum uses to track the signals) are approximately 40dB (ten thousand times) stronger than GPS signals. For positioning, Rosum does not require that a TV signal be strong enough to be viewed on a TV set. 50dB of processing gain allow us to use even weak TV signals for location.
Frequency
GPS signals are transmitted at a frequency (1.575 GHz) which is strongly attenuated by buildings and other man-made structures. TV signals, in comparison, are broadcast at much lower frequencies (50-700 MHz). At these frequencies, signals are able to achieve building penetration for in-building TV viewing and Rosum positioning.
Frequency Diversity
Since each TV tower typically broadcasts more than one channel, the Rosum receiver will have a better chance of acquiring a signal given that these channels are broadcast at different frequencies. Rosum can choose the best channels from each tower to compute the user’s location.
Bandwidth
In general, the wider the bandwidth of the signal, the more accurately one can resolve multipath, or the reflected signals that characterize urban and indoor environments. The bandwidth of broadcast television ranges from 6 MHz to 8MHz depending on the standard. In contrast, the bandwidth of the GPS satellite signal is 1MHz. This provides roughly a 6:1 bandwidth advantage, and a 6:1 advantage in the mitigation of signal multipath. (source: http://www.rosum.com/)