Satellite Radio: The Next Communications

Revolution?

David Bultman, Student Member, IEEE

Abstract – Various aspects of the emerging satellite radio

technology are presented. To set the stage, the desirability of

satellite radio and the governmental rulings are presented.

The various challenges to broadcasting from satellites which

each service provider must surmount are presented in detail.

In depth discussions of the XM Radio and Sirius Radio

systems follow as a means of evaluating the efficiency and

effectiveness of each.

I. WHY SATELLITE RADIO?

Radio is one of the few services in the nation which

resisted the digital revolution. Television, wireless phones,

and other devices have embraced digital communications

technologies as a means to further bolster the robustness of

their systems.

Today, radio generally falls into two categories. AM

(Amplitude Modulation) radio broadcasts fairly low

frequencies. AM radio is very susceptible to interference and

propagation variability. These problems allow AM radio to

cover a fairly wide area but prevent Am radio from providing

a reliable service over that area. The narrowband nature of

AM stations prevents their broadcasts from containing any

significant amount of audio quality.

FM (Frequency Modulation) was the response to the

problems of AM radio. FM radio uses higher frequencies and

more bandwidth per station. The result is better audio quality

with somewhat reduced susceptibility to interference. FM

radio, however, has less range than AM radio.

Clearly a modern digital alternative to AM and FM radio is

needed. This new digital service should provide high quality

audio to a wide geographical area using a very robust system

if it to compete effectively with current radio and other audio

sources such as CDs and digital cassettes.

II. GOVERNMENT ACTION

The Federal Communications Commission (FCC) set aside

in the Code of Federal Regulations a section defining the

necessary qualifications to be licensed for its new Satellite

Digital Audio Radio Service (SDARS) classification. The

qualified applicants had to “describe in detail the proposed

satellite digital audio radio system, setting forth all pertinent

technical and operational aspects of the system, and the

technical, legal, and financial qualifications of the

applicant.”[9]

The applicants also had to give specifications for receivers,

compression rates, and meet various milestones. At the end

of one year, from the date of authorization, the applicant has

to complete contracting for construction of its first satellite or

begin the actual construction. At the end of two years the

second satellite, if applicable, must be contracted or in

construction. At the end of four years at least one satellite

must be in orbit and operational. At the end of six years the

entire satellite system must be in full operation. The

applicants are also forced to service, at least, the 48

contiguous states of the United States.

At the time, four companies were qualified to compete for

the new SDARS licenses. The companies are: Satellite CD

Radio, Inc. (now Sirius Satellite Radio), Primosphere Limited

Partnership, Digital Satellite Broadcasting Corporation, and

American Mobile Radio Corporation (now XM Satellite

Radio).

The original proposed frequency band extended from 2310

MHz to 2360 MHz. Congress changed the band November

of 1996 by deciding one half of the proposed band be

auctioned for terrestrial services instead. The new SDARS

band then extended from just 2320 MHz to 2345 MHz. The

25 MHz left in the SDARS band was not enough for four

SDARS operators. Congress had effectively allowed only

two of the four qualified applicants to be licensed for use in

the band.

The result was an FCC auction of the remaining bandwidth

in April of 1997. Satellite CD Radio, Inc. won one of the

licenses with a bid of $83,346,000 and a down payment of

$13,669,200[8]. American Mobile Radio Corporation won

the other license with a bid of $89,888,888 and a down

payment of $14,977,777[8]. American Mobile Radio

Corporation (XM Radio from now on) uses the upper half of

the spectrum from 2332.5 MHz to 2345 MHz. Satellite CD

Radio, Inc. (Sirius Radio from now on) uses the lower half of

the spectrum from 2320 MHz to 2332.5 MHz. The frequency

distribution can be seen below in Figure 1.

Figure 1. The SDARS Spectrum[18]

III. TECHNICAL ISSUES WITH SATELLITE

BROADCASTS

A. The Problems to Overcome

The SDARS’ operators target audience is consumers in a

mobile platform (essentially automobiles). This raises a

unique problem. The antenna used for reception of can not

be overly expensive or else consumers will not want the

service. XM Radio and Sirius Radio are forced to abandon

special high gain antennas and complicated satellite tracking

mechanisms to keep the receiving antenna pointed at the

satellite. The providers are forced to use omni directional

antennas very similar to the antennas used for mobile phones.

Ruling out special antennas gives rise to the importance of

schemes for mitigating the three basic reception problems of

satellite communications.

As the mobile receiving platform moves, from time to time

the broadcast signal from a given satellite will be blocked

completely. This affect depends upon the vehicle’s

movement, the satellite’s movement, and the satellite’s angle

of elevation. The faster a vehicle moves the move possible

blockages it comes into contact with but the length of those

blockages decreases. For non-geostationary satellites, the

path which the broadcast travels to the mobile receiver

changes over time which further complicates the possibilities

for blockages. The movement of the satellite is much less of

a problem than the movement of the vehicle, however. As a

satellite’s angle of elevation increases with respect to the

mobile receiver the satellite becomes closer to being directly

overhead of the mobile receiver. It is obvious that a signal

which travels essentially vertically (as in the case of a very

high angle of elevation) to the receiver is much harder to

block in some ways. Conversely, a low angle of elevation

will allow the broadcast signal to reach into tunnels and under

overpasses better.

The broadcast signal can also be attenuated by foliage.

Foliage acts, to an extent, in the same way complete

blockages work with respect to the motion of the mobile

receiver, the motion of the satellite, and the angle of elevation

of the satellite. However, foliage is unique in that the amount

of attenuation can depend on the frequency of the signal and

the angle at which the signal strikes the foliage. Foliage can

also reflect a signal with a random phase shift. This is related

to multipath interference. Multipath interference occurs

when the broadcast signal bounces off of any variety of

objects with varying degrees of attenuation and phase

shifting. The receiver picks up these other paths as well as

the original broadcast signal and must determine how to

interpret the multiple signals as shown in Figure 2. The

reflected signals can even tend to cancel the legitimate

broadcast signal.

Figure 2: An Example of Multipath Interference [1]

Research has been conducted into the effect of foliage.

“The transmission margin necessary to overcome

multipath fading or attenuation from foliage has been

both measured and estimated by experts to be in the

range of about 9 to 12 dB for satellite radio broadcast

systems operating at UHF frequencies with reception at

mobile platforms having roughly a 20 degree or more

elevation angle to the satellites. Fortunately, multipath

and attenuation from foliage seldom occur

simultaneously. However, the need for 9-12 dB

transmission margin means that satellite transmitter

power must be increased by a factor of 8 to 12 over its

initially high level.”[1]

B. Solutions to the Problems

There are a number of very inventive ways to alleviate the

problems associated with satellite broadcasts. The first

solution is called spatial diversity. Implementing spatial

diversity entails having more than one legitimate broadcast

signal path which the receiver can draw on. The simplest

way to accomplish this is to have more than one satellite as

shown below in Figure 3.

Figure 3: Implementing Spatial Diversity [1]

Spatial diversity helps to solve each of the three basic

reception problems. As seen in Figure 3, the probability of

completely blocking or attenuating multiple broadcast signals

at the same time, as the mobile receiver moves, is fairly

unlikely. Spatial diversity also helps reduce the effect of

multipath inference. By providing two legitimate broadcast

signals the receiver, in some cases, is able to ignore one of

the signals will all of its reflections in favor of a much

cleaner second signal.

Another solution is called frequency diversity. In a

frequency diverse system the single broadcast signal is sent

via two or more frequencies (preferably spatially diverse) to

the receiver. This solution is primarily aimed at stopping

multipath interference which, as stated before, can be

frequency selective. An example of frequency diversity is

shown in Figure 4.

Figure 4: An Example of Frequency Diversity [1]

The third solution is called time diversity. Time diversity

is employed is systems already having spatial diversity and

frequency diversity. In a time diverse system, one of the two

broadcast signals is delayed in time before it is broadcast. So

while one signal is at second X in the program the other

signal is at second X – C. Time diversity allows the receiver

to experience fairly severe blockages of both signals at the

same time. The concept of time diversity is demonstrated in

Figure 5.

Figure 5: An Example of Time Diversity [2]

In the time diverse system, the longer the broadcast delay

between the signals is the longer either of the signals can be

completely blocked from reception at the receiver. The

broadcast delay is typically between 0.5 seconds and 5

minutes [2].

The last solution is a repeater station. There are some

places (generally within cites or within very mountainous

territory) where even the previous 3 solutions can not ensure

a reliable signal fro the receiver. Repeater stations are set up

to receive the satellite broadcast and then rebroadcast at an

entirely new frequency (which further adds to the frequency

diversity of the overall system). Recall from Figure 1 that

some of the SDARS spectrum was reserved by both XM

Radio and Sirius Radio for repeater stations. The operation

of repeater stations is shown below in Figure 6.

Figure 6: The Compete System with Repeater Stations [2]

IV. ACTUAL IMPLEMENTAIONS

A. XM Radio’s System

XM Radio owns three Boeing HS 702 satellites of which

two are deployed in a geostationary orbit (about 22223 miles

above the earth). One satellite is at 85 degrees west

longitude and the other is at 115 degrees west longitude. An

artist’s rendering of the XM Radio system is shown in Figure

7.

Figure 7: The XM Radio System [16]

Each satellite in XM Radio’s system essentially covers one

coast of the United States. By spreading the satellites over

such a wide distance XM Radio is implementing spatial

diversity.

XM Radio claims the Boeing HS 702 satellites it owns

transmit an effective energy of 10 MW. By using very high

power satellites XM Radio is compensating for multipath and

attenuation effects. The satellites have a 45 degree angle of

elevation. Recall from the previous discussion how the angle

of elevation affects reception. Although XM Radio chose a

typical angle of elevation, the angle is such that a significant

number of repeaters are necessary. In fact, XM Radio has

approximately 1500 repeaters covering about 70 markets.

These repeaters are mostly 2 kW stations. These are not very

powerful repeaters compared to a standard AM or FM station

which can run up to 100kW.

Frequency diversity is implemented in the XM Radio

system by giving each of the satellites and the repeater

stations a different broadcast frequency. Again recall Figure

1. XM Radio also employs a time diversity scheme although

the exact timing is undisclosed.

XM Radio is headquartered in Washington, D.C. At its

headquarters it has 82 studios. The channel line up includes

100 channels, 60 of which are commercial free. There are 6

channels dedicated to decades, 5 to country music, 15 to hits,

10 to rock, 7 to urban, 6 to jazz and blues, 4 to dance, 5 to

latin, 6 to world, 4 to classical, 2 to kids, 12 to news, 5 to

sports, 3 to comedy, and 10 to talk and variety channels.

Currently Sony, Pioneer, Alpine, and Audiovox produce

XM Radio ready receivers. The receivers range from $100 to

$2100 with antennas costing in the neighborhood of $100.

GM, Isuzu, Nissan, Volkswagen, and Honda have deals with

XM Radio to install satellite radio ready receivers in select

models. The XM Radio service runs $9.95 per month.

To be profitable, XM Radio estimates it will need 4 million

subscribers. At the end of March 2002 XM Radio has signed

up about 76,000 people which is ahead of schedule. By the

end of the year they hope to have 350,000 subscribers.

B. Sirius Radio’s System

Sirius Radio owns 4 SS/L-1300 satellites of which 3 are

deployed in an inclined elliptical constellation. In the

constellation each satellite spends about 16 hours of every

day over the continental United States. The Sirius Radio

system is shown in Figure 8. Although the Sirius satellites

are constantly on the move they can be considered to be at

100 degrees west longitude while they are over the United

States. The Sirius satellites tend to be over the center of the

United States as opposed to the coastal approach of XM

Radio. Sirius is implementing spatial diversity but to a lesser

extend than XM Radio. The Sirius satellites have an angle of

elevation of 60 degrees which is much better than XM Radio.

It appears Sirius traded off some of the spatial diversity for a

better angle of elevation which hopefully provides equal

quality service.

The Sirius satellites are of lower power than the XM

satellites. This is partially made up for by the angle of

elevation. Sirius Radio, like XM Radio, requires repeaters.

Sirius Radio has about 105 repeaters serving 46 markets.

These repeaters are significantly more powerful than XM

Radio’s. The Sirius repeaters are up to 40 kW. Sirius

implements frequency diversity (as in Figure 1) and a time

diversity scheme like XM Radio.

Figure 8: The Sirius Radio System [17]

Sirius Radio is headquartered in New York City. Sirius

Radio has 75 studios. The channel line up also includes 100

channels, all of which are commercial free. There are 8 pop,

11 rock, 6 country, 8 R&B or Urban, 4 dance, 7 jazz, 5 latin,

3 classical, 8 variety, 14 news, 5 sports, 5 hispanic, 9

entertainment, and 7 lifestyle channels.

Currently Kenwood and Clarion produce Sirius Radio

ready receivers. The receivers range from $180 to $2800

with antennas costing the same as XM Radio’s. Sirius Radio

has deals with Ford, DaimlerChrysler, BMW, Mercedes,

Mazda, Jaguar, and Volvo to install satellite radio ready

receivers in select models. The Sirius Radio service runs

$12.95 per month. Sirius Radio is not fully covering the

United States at this time but estimates the full service will be

launched in July of 2002.

V. ARE THEY WORTH IT?

From all indications, the services live up to their claims of

nonstop high quality radio. Reviewers thus far, have noted

that signal losses are hard to generate and fairly short in

length. The biggest complaints are from very urban areas

like New York where the immense urban jungle has not been

pierced by repeater towers as of yet.

Perhaps a better question is whether consumers will be

willing to pay to listen to the radio when terrestrial radio

stations go digital was well as they hope to do in the next few

years. In any event, satellite radio will spark the digital

revolution in radio industry which has been so long overdue.

VI. REFERENCES

[1] Robert D. Briskman, John M. Seavey, and Paul Medeiros,

“Radio frequency broadcasting systems and methods using

two low-cost geosynchronous satellites and hemispherical

coverage antennas,” U.S. Patent 5485485, January 16, 1996.

[2] Robert D. Briskman, “Mobile radio receivers using time

diversity to avoid service outages in multichannel broadcast

transmission systems,” U.S. Patent 5592741, January 7,

1997.

[3] Daniel Lieberman, “Satellite multiple access system with

distortion cancellation and compression compensation,” U.S.

Patent 5720039, February 17, 1998.

[4] Daniel Lieberman, “Satellite multiple access system with

distortion cancellation and compression compensation,” U.S.

Patent 5745839, April 28, 1998.

[5] Robert D. Briskman, “Satellite broadcast system

receiver,” U.S. Patent 5794138, August 11, 1998.

[6] Robert D. Briskman, “Digital radio satellite and terrestrial

ubiquitous broadcasting system using spread spectrum

modulation,” U.S. Patent 5864579, January 26, 1999.

[7] Robert D. Briskman, “Satellite broadcast receiver

system,” U.S. Patent 6023616, February 8, 2000.

[8] Federal Communications Commission Report No. AUC

97-05, Auction No. 15, “FCC announces auction winners for

digital audio radio service,”

wireless.fcc.gov/auctions/15/releases/da970656.pdf, April 2,

1997

[9] Code of Federal Communications 47CFR25.144,

“Licensing provisions for the 2.3 GHz satellite digital audio

radio service,” October 1, 2001.

[10] FCC Auctions Division, “2.3 GHz spectrum band

allocation,”

http://wireless.fcc.gov/auctions/data/bandplans/wcsband.pdf.

[11] Leslie Taylor Associates, Inc., “Regulatory update:

satellite digital audio radio service (SDARS),”

www.lta.com/sdars.html

[12] Jim Wagner, “Wireless providers in ‘Sirius’ Trouble,”

ww.internetnews.com/isp-news/article/0,,8_992321,00.html,

March 15, 2002.

[13] Renae Merle, “XM Satellite Radio reaches 30,000

users,” www.newsbytes.com/news/02/173464.html, January

8, 2002.

[14] Yahoo!, Inc., “Satellite and digital radio news stories,”

dailynews.yahoo.com/fc/Tech/Satellite_and_Digital_Radio/.

[15] Kevin Bonsor, “How satellite radio works,”

www.howstuffworks.com/satellite-radio.htm.

[16] XM Satellite Radio, www.xmradio.com/.

[17] Sirius Satellite Radio, www.siriusradio.com/.

[18] David H. Layer, “Digital radio takes to the road,”

www.spectrum.ieee.org/WEBONLY/pressrelease/0701/0701

dig.pdf.