In-Building Location Technology For LTE By William C. Y. Lee Peking University, China In-Building Technology Forum Denver, Colorado January 18-20, 2011

Why In-Building Location Technologies GPS can not be used for in-building location Many users are using handsets inside building Most young people only have cell phones and do not have landline phones. In-building locations are needed for e-commerce use. In-building locations are needed for emergency use. In-building locations are helping for system performance

What are Existed In-Building Location (IBL) Terchnologies Use signal strengths received at base stations (BSs) to figure out the location of a desired mobile unit (MU) Use Time of Arrival (TOA) Uplink Time Difference of Arrival (U-TDOA) Use Angle of Arrival (AOA) Most technologies need all the base stations to be synchronized

New Proposed IBL Technology (1) Try to obtain the distance measurement from base station (BS) to mobile unit (MU) Use the unique reference signals from the LTE system Transmitting a time marker (a marked symbol) on a reference signal at a BS modulated on PDCCH (Physical Downlink Control Channel) to MU. The reference signal with a time marker received by MU will be transmitted back on PUCCH (Physical Uplink Control Channel) to BS.

New Proposed IBL Technology (2) The PUCCH will be demodulated at BS The reference signal with a time marker is then obtained at the BS receiver Measure the time difference between the two time markers, T1 and T2, one is when PDCCH is sent and one is when PUCCH is received . Time difference T = T2 – T1 – = time marker of the reference signal stays at MU

Calculation of Distance The distance D between BS and MU D = (T /2 ) x v v = EM wave speed The light speed in vacuum = 3x 10*8 m/s = 3x10*5km/s v can be measured at the location of the system network after the system is built, and be used to calculate the distance D. This technology was considered in AMPS

Supervisory Audio Tones in AMPS Supervisory Audio Tones (SAT) consists of three tones, 5970Hz, 6000Hz and 6030Hz Supervisory Audio Tones (SAT) are used to serve for three purposes : 1) Acting as a dial tone in the landline phone 2) Used for identifying the Base Stations (BS) by assigning a SAT for each BS. 3) It was considering in the original plan for measuring distances of mobile units

Using SAT of AMTS for Location In 1970, no GPS was build AMPS was the first cellular system designed by Bell Labs in 70’s and deployed in 1984. It was an analog radio system. The Locations of MSs were very important for system performance known by the engineers. The error of measuring MS distance in the spec can be tolerated

SAT of AMPS For Location Finding The frequencies with their allowed errors in three SATs are 5970 Hz +/- 15 Hz 6000 Hz +/- 15 Hz 1 Hz = 1 cycle/s 6030 Hz +/- 15 Hz In SAT, converting frequency error into distance error a = 3x 10 *5 km/6000 cycle = 50 km /cycle b = 3x 10 *5 km/6015 cycle = 49.87km/cycle The error a-b = 124.688 m / 50 km, or 90 ft/ 8 miles

The difficulty of using SAT for RTL The error of using RTL (real time location) in the system based on the spec is about 90 ft over 8 miles. It should be OK. But the analog system operation was hard to maintain within the specified error. Besides, there were many other errors generated from the early analog radio systems. Only three SATs could be used to estimate a location of MS. The MS location can not be accurately found by using triangulation of three BSs. The feature was abandoned in AMPS.

Advantages of Using The New IBL It is using in digital systems There are 512 reference signals in LTE. Each one has assigned to each sector of each BS or access point. The incremental response time is 1 ms in LTE. Therefore, we can use multiple triangulation scheme to estimate the location of MS. It can be applied in non-synchronized systems

3GPP’s Status for LTE Spec As today, 3GPP’s preparation are currently underway to standardize an optimized interface format for base station’s transmitting signals in LTE It can be the right time to make a proposal to introduce the new IBL technology as a new feature to LTE

Summary This is just a proposed IBL technology. The IBL technology can be built in the LTE system. The IBL technology does not need a common clock as in a synchronized system. It is easy to be implemented. It need more research work for IBL accuracy.

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