# Base Station Antenna Tilt and Path Loss

Path loss is basically the difference in transmit and receive powers of a wireless communication link. In a Free Space Line of Sight (LOS) channel the path loss is defined as:

L=20*log10(4*pi*d/lambda)

where ‘d’ is the transmit receive separation and ‘lambda’ is the wavelength. It is also possible to include the antenna gains in the link budget calculation to find the end to end path loss (cable and connector losses may also be factored in). Antenna gains are usually defined along a horizontal plane and vertical plane passing through the center of the antenna. The antenna gain can then be calculated at any angle in 3D using the gains in these two planes.

Although 3D antenna gains are quite complex quantities simplified models are usually used in simulations e.g. a popular antenna Kathrein 742215 has the following antenna gain models [1] along the horizontal and vertical planes:

Gh(phi)=-min(12*(phi/HPBWh)^2, FBRh)+Gm

Gv(theta)=max(-12*((theta-theta_tilt)/HPBWv)^2, SLLv)

where

Gm=18 dBi
HPBWh=65 degrees
HPBWv=6.2 degrees
SLLv=-18 dB

We are particularly interested in the gain in the vertical plane and the effect of base station antenna tilt on the path loss. We assume that the mobile antenna station has uniform gain in all directions. The path loss can be then calculated as:

L=20*log10(4*pi*d/lambda)+Gv(theta)+Gh(phi)

where we have assumed that Gh(phi)=0 for all phi (this is a reasonable simplification since changing the distance along the line of sight would not change Gh(phi) ). Using the above expression the path loss in free space is calculated for a frequency of 1805 MHz, base station antenna height of 30 m and an antenna tilt of 5 degrees.

Effect of Antenna Tilt on Path Loss

It is observed that there is a sudden decrease in path loss at distances where the antenna main beam is directed. If the antenna tilt is increased this behavior would be observed at smaller distances. Since we have used a side lobe level that is fixed at -18 dB we see a rapid change in behavior at around 100 m. If a more realistic antenna model is used we would see a gradual decrease in path loss at this critical distance.

[1] Fredrik Gunnarsson, Martin N Johansson, Anders Furuskär, Magnus Lundevall, Arne Simonsson, Claes Tidestav, Mats Blomgren, “Downtilted Base Station Antennas – A Simulation Model Proposal and Impact on HSPA and LTE Performance”,
Ericsson Research, Ericsson AB, Sweden. Presented at VTC 2008.

# 4G LTE Coverage within Virginia

Since our last post on Verizon LTE coverage within California, Verizon has removed the LTE Coverage Map from its site. Now it only gives a list of cities that have 4G LTE service (just like T-Mobile). So we now move from the West Coast to the East Coast i.e. Virginia. The state that is home to Virginia Tech, one of the finest schools in the country and a breeding ground for Wireless Engineers. It is thus somewhat of a shock to see that Verizon Wireless has no 4G LTE footprint in the state of Virginia. The only place that it intends to deploy 4G in near future is Bristol Virginia. It claims that by the end of 2013 it would have 4G coverage throughout the US where 3G service is currently available.

As in California T-Mobile has a much wider coverage with many smaller cities getting 4G service. The list includes: Alexandria, Mclean, Newport News, Norfolk, Petersburg, Portsmouth, Reston, Richmond, Roanoke and Lychburg. So although Verizon might be winning the speed race it is definitely not winning the coverage race (at least in CA and VA). And with AT&T T-Mobile merger also a possibility early next year Verizon is set to face some stiff challenge.

Given below are the results of a 4G speed test conducted by PC Magazine in the Northeast.

4G LTE Speed Test

The above results show that in areas where 4G coverage is available Verizon allows for average download speeds that are twice that of T-Mobile. The upload speeds are somewhat similar. Overall Verizon is by far the best in terms of the Mobile Speed Index, with T-Mobile in second spot and AT&T at third.

# T-Mobile 4G Coverage within US

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.