Tag Archives: LTE

T-Mobile 4G Coverage within US

HSPA, LTE, ,

T-Mobile claims to be serving 4G to 152 markets with 170 million POPs across the US. The technology that T-Mobile is using is HSPA+ which achieves data rates comparable to those achieved by 4G LTE technology being used by Verizon. With this technology (HSPA+21 and HSPA+42) end users can experience average download speeds of 5Mbps and peak download speeds of 12Mbps. However the future of T-Mobile hangs in the balance now as the AT&T and T-Mobile merger is being debated at the FCC.

T-Mobile LTE Coverage

Although the above figure seems to suggest that T-Mobile 4G service is available throughout US it must be noted that the service is actually available only in high density urban areas where operators make most of their revenue. This means that 4G service would not be available on most of the highways. So the 4G service must at this point compete with not only other wireless services but also with DSL and Cable.

Just to get an idea of the coverage we look at the list of cities getting 4G service in California (as claimed by T-Mobile). The list includes: Anaheim, Burbank, Fresno, Glendale, Irvine, Los Angeles, Long Beach, Merced, Modesto, Monterey, Napa, Oakland, Ontario, Palm Springs, Sacramento, San Diego, San Francisco, San Jose, Santa Rosa-Petaluma, Salinas, Stockton, Vallejo-Fairfield, Visalia.

It seems that the T-Mobile 4G service in California is much more widely spread than Verizon LTE (see previous post) with many smaller cities such as Stockton, Modesto, Santa Rosa and Visalia also getting 4G service.

POP: Point of Presence.

Verizon 4G LTE Deployment Within California

LTE, , ,

We have previously looked at the birds eye view of 4G LTE coverage within the US. We know that Verizon 4G services are now available to more than 50% of the US population. However, geographically, the service is only available in very small islands of population. Now, we take a closer look at 4G LTE coverage within California.

LTE Coverage in CA

We see that the coverage is available in most of the population centers such as Sacramento, San Francisco, Oakland, San Jose, Fresno and Bakersfield. Further south the coverage is also available in areas around Los Angeles and San Diego. But what is not shown on this map is that there is no coverage in many smaller cities such as Stockton, Modesto, Santa Rosa and Visalia. Also there is no coverage on the highways connecting these cities e.g. there is no coverage on I-5 which runs along the length of the state.

Bottomline: You may get very good LTE coverage when you are at home but don’t expect the same when you are on the highway. You will most probably have to fall back to 3G.

 

Verizon 4G LTE Deployment within the US

LTE, ,

Verizon Wireless 4G LTE is now available to 160 million people with coverage in 117 cities within the US. This has been achieved within eight months of the initial deployment. Verizon hopes to increase the coverage to 185 million people by the end of 2011. The company claims that with its current deployment strategy users can experience data rates of 5-12Mbps on the downlink and 2-5Mbps on the uplink. When users do not have access to the 4G LTE network the phones will automatically switch to 3G which is available around most of the US.

LTE Coverage

This push to 4G creates a big gap between the developed and underdeveloped parts of the world where many nations have still not migrated from 2G to 3G.

LTE Spectrum Allocation

LTE, ,

LTE devices operate in either of two modes: TDD (time domain duplex) or FDD (frequency domain duplex). In FDD transmission and reception takes place at different frequencies whereas in TDD transmission and reception takes place at the same frequency but different time slots. The are separate frequency allocations for these two modes but some bands are common between the two modes. Given below are the frequency allocations for FDD.

LTE FDD

There is suitable separation between the uplink and downlink frequency bands (at least 10MHz) so that the transmitted signal does not feedback into the receiver. It is extremely difficult to build a device that works in all of these 22 bands (due to limitations of practical antennas).  Practical devices would at most be quad-band or penta-band. So an LTE device that would work in all parts of the world is more of a dream!

Average Cell Throughput Calculations for LTE

Channel Capacity, LTE, ,

Average Cell Throughput requires the following simulation results

• Average SINR distribution table (system level result), which provides the SINR probability

• Average throughput or spectral efficiency versus average SINR table (link level result)

For urban channel model and a fixed inter-site distance of 1732m,downlink throughput for LTE for different values of SINR is shown below.

MCS vs SINR

Average Cell Throughput=Σ(Pi*Ri)

where

Pi=Probability of occurrence of a specific SINR value at cell edge obtained using simulations
Ri=Average throughput corresponding to SINR range

Let us consider the following distribution for the SINR at the cell edge:

P1=0.5 (SINR=1.50-3.50 dB)
P2=0.25 (SINR=3.50-7.00 dB)
P3=0.15 (SINR=7.00-9.50 dB)
P4=0.10 (SINR=9.50-11.50 dB)

Cell Throughput=(0.50*4)+(0.25*6)+(0.15*8)+(0.10*12)=5.9 Mbps

Note: This throughput is much less than the theoretical maximum which assumes that the full 20 MHz bandwidth is being utilized in a 4×4 MIMO configuration.

 

LTE Data Rate Calculation

Capacity, LTE, ,

Peak LTE data rate can be calculated using the following parameters:

1 Time-slot=0.5 ms (i.e 1 Sub-frame = 1 ms)
1 Time-slot=7 Modulation Symbols (when normal CP length is used)
1 Modulation Symbol=6 bits; if 64 QAM is used as modulation scheme

Data rate for a single carrier=Number of symbols per time slot*Bits per symbol/Duration of a time slot=7*6/0.5e-3=84kbps

If 1200 carriers (100RBs) are used then the aggregated throughput would be=1200*84kbps=100.8Mbps

If 4×4 MIMO is used then the capacity would increase four fold to=403.2Mbps

With 3/4 channel coding the data rate would be reduced to=302.4Mbps

Note:

1. A Resource Block (RB)=12 Carriers

2. Actual data rate would depend upon the instantaneous channel conditions and number of users sharing the resources e.g. going down from 64QAM to QPSK in adverse channel conditions would reduce the data rate from 302.4Mbps to 100.8Mbps.  Changing the code rate from 3/4 to 1/3 would further reduce the data rate to 44.8Mbps.