CDPD

CDPD (Cellular digital packet data) was one of the most exciting ways of transmitting data. There were great expectations of CDPD being great anytime and anywhere access to the Internet. More recently other methods of Internet access have come out and seem to be more appealing to most companies.

CDPD uses cellular voice channels to transmit data. Data is transferred during the idle time in these voice channels. Cellular digital packet data uses channel-hoping techniques to utilize gaps of unused channel time for data transmission. Users share the same data stream as they transmit their data packets. CDPD uses IP and CLNP (Connectionless network protocol). CDPD was found interesting because it made incredible leaps in the cost of data packet transmission. Previously, when one would send information one would get charged by the minute, even if the transmission took a total of 20 seconds. Now, CDPD does not charge by the minute, but rather by the byte.

Products that use CDPD

Ericsson has recently come out with a phone that uses TDMA (which will be talked about later) and CDPD. Ericsson calls this piece of equipment the R280. The phone will be run on large networks that will be provided by carriers such as AT&T (Palenchar 32). The phone is equipped with a microbrowser, three hours of talk time and 120 hours of standby time. Because of the implementation of newer technologies, AT&T is one of the few companies that still use CDPD. One might believe that this is because they put some much money into it that they must continue to use it.

CDPD in the market

Although CDPD was expected to save the customer dollars by charging by the byte, CDPD did not save the carrier any money. Few carriers would say that the overall cost of the infrastructure and the cost of running the business was way to expensive for the carriers own good (Zsigo). At least 1/3 of CDPD’s sales have come from the public safety market. Public safety officers love the effortless communications that CDPD provides. In addition, CDPD never really had a problem with complaints, and it always has been considered a technological marvel.

CDMA

Internet and wireless users have been experienced rapid growth. Each year we have more of a need to incorporate wireless Internet access. The following table expresses the increased Internet and wireless users:

(From http://www.cdg.org/frame_tech.html)

This is how you would get a wireless connection to the Internet using CDMA:

CDMA (Code Division Multiple Access) is experiencing rapid growth in the voice and data world.

The spectrums for CDMA are 1850MHz to 1910MHz and 1930MHz to 1990MHz. CDMA is a type of radio communications that incorporates digital technology. It also uses spread spectrum technology (direct sequence) to send and receive transmissions. Each transmission signal is given its own one of its kind code, called chips. The chips are imbedded into the bits signal. The process of adding the chips to the bit sequence is called Xor. After the first Xor, the receiver Xors again and all 1’s or 0’s will come up depending on the bit that was sent. This is how the receiver determines what bit was sent to it.

Using CDMA digital phones, voice quality goes up. The voice quality of CDMA digital phones is not much different than that of landline phones. CDMA phones use special microprocessors that work with CDMA to give a high quality sound. Next, security is always an issue with cellular phones. CDMA basically prohibits eavesdropping. Because it was originally designed by the military, the words CDMA and high quality security are synonymous. Because each little bit that is transferred is spread on a wide spectrum of frequencies, and because chips are used in the physical layer, high security is just about guaranteed. CDMA also prohibits a network busy signal. CDMA allows the provider to have more customers, thus eliminating the bottleneck (Qualcomm website-see bibliography).

CDMA tends to be very competitive in the areas where interference comes into play heavily. One problem to be noted of CDMA is that it experiences a problem called the near-far problem. The near-far problem occurs when near users receive a signal at a much higher power than the far out users. This problem does not seem to be much of a factor for terrestrial based cellular networks.

CDMA uses wireless IP. Why is this good? Wireless IP basically creates a new generation of services. One can use a wireless device whether it is a computer or cellular phone, to use the Internet.

Multicarrier CDMA vs. single carrier CDMA

Mulitcarrier wideband CDMA with spread spectrum and direct sequence occurs when some data is combined with a spreading sequence. The result will be many carriers instead of a single carrier (Milstein 25). The receiver contains a correlator for each of the carriers, and outputs them as if they were comparable to a single carrier. A multicarrier, just like a single carrier, does not experience multipath fading. Next, the multicarrier system can avoid narrowband interference. The narrowband interference can be avoided by simply not using the carriers that have the narrowband interference on them. Finally, a lower chip rate is required for the multicarrier system. The bandwidth of the system is divided among the carriers, so each carrier frequency is modulated with a chip sequence that is the number of carriers times as long as the rate of a single carrier. This could lead to a slower type of signaling processing, thus making it possible to use a lower powered consumption device (Milstein 25).

Wireless Local Loops

Many developing counties do not have the time and/or money to put in a desperately needed phone system. So, they have turned to the cellular market. Cellular companies can now use the networks they have in place in order to provide a residential service. First, the advantage of deploying CDMA in a country for fixed telephony service is CDMA has an advantage over AMPS and other systems because it can provide much more capacity--15-20 times more capacity than that of AMPS and 4 to 5 times that of GSM. Some of the countries that have actually deployed CDMA are: Brazil, China, Democratic Republic of Congo, Dominican Republic, Haiti, Mauritius, India, Mongolia, Nigeria and Russia (http://www.cdg.org/frame_tech.html).

Users of CDMA

Now becoming one of the most prevalently used technologies concerning wireless data transmission, CDMA now has over 35 million users.

QUALCOMM-HDR

Qualcomm has become the largest producer of CDMA products and services, and is also the leader in mounting the technology (QUALCOMM). CDMA is also one of the largest licensers of CDMA-licensing CDMA to 75 different companies. It deploys HDR (High Data Rate) services and high-grade voice quality. HDR is compatible with Qualcomm’s cdmaOne ™ technology, which is capable of supplying a 1.8 Mbps wireless connection to the Internet. HDR uses a 1.25 MHz bandwidth and uses IP (Internet Protocols) so in turn it is flexible.

About cdmaOne and cdma2000:

(From http://www.cdg.org/frame_tech.html)

Also, CDMA has doubled it’s customer base in the last two years (Blume). Because of this rapid and massive increase, a large demand for high-grade voice quality and data services are in demand. 3G (third generation) standards (cdma2000 – for example) will provide services such as Internet access, e-mail and video conferencing (Blume). A way to move towards the faster and more abundant connection is to rotate towards cdma2000, from cdmaOne. Using handsets that were designed for cdmaOne will be compatible with cdma2000, but the handsets will not be able to perform at the cdma2000 speed (up to 2 Mbps).

Moving towards 3G, cdma2000 will provide new and interesting features. New features will include:

· Standby times increased by 50 – 100%

· Color screens

· WAP

· Text input

CDMA has increased its users by 100% in the last two years and has increased its coverage over the world:

Sprint PCS

Sprint has come out with a CDMA phone that allows connection to the Internet. The SCH-3500 offers high voice quality as well as a connection to the Sprint PCS Wireless Web. The phone allows users to browse text versions of popular websites through the Internet. It also allows the user to check email and see news updates such as weather and sports scores. The phone can also connect to a laptop and serve as a wireless modem for the Internet or corporate Intranet access. The extended battery allows for 5 hours of talk time in the CDMA mode as well as 230 hours of standby time.

Motorola

Motorola has recently come out with MIX (Mobile Internet Exchange) that provides end-to-end solutions to CDMA, GSM, and TDMA. Motorola, in its StarTac mobile phone, has used MIX in its micro browser. MIX allows Motorola to integrate voice and data. The phones can convert text to voice, which allows the user to listen to e-mail that was sent to him/her, or to listen to text while the user is browsing. Motorola allows other carriers to buy the MIX platform and integrate it in their networks, or they can use Motorola as a service provider (Holt).

TDMA

TDMA (Time Division Multiple Access) is a digital technology that takes three different signals and multiplexes them into a single channel. TDMA develops unique time slots in order to avoid interference. TDMA takes a single frequency channel for a short period of time and then transfers it to another channel. A transmitter takes digital samples and makes them occupy different time slots, at different times, in several bands (http://www.webproforum.com/tdma/topic02.html).

The following is a simple diagram displaying TDMA:

From (http://www.webproforum.com/tdma/topic02.html)

Weaknesses of TDMA

One of the major problems with TDMA is that it designates time slots whether or not there is anyone talking. So you have a possibility of wasted bandwidth. TDMA’s solution to this is through Extended TDMA where the sender fills a buffer with information and the multiplexer scans the buffer. When the multiplexer scans the buffer, it sees if that sender has any thing to send. If its does, the multiplexer allocates the bandwidth. If not, no time slot is designated to that particular sender. This technology basically doubles the efficiency of regular TDMA.

Advantages of TDMA

· Will not experience interference from other transmissions, because it separates users in time

· Provides user with extended talk time because it only transmits 1/3 to 1/10 of the time.

· Offer substantial savings

· Most cost effective way of changing from an analog system to digital system.

From (http://www.webproforum.com/tdma/topic04.html)

Disadvantages of TDMA

· Users have a predefined time slot

· If roaming, the caller might be cut of when moving to another cell if all the time slots are taken.

· If all the time slots are taken before making the call, the caller will not receive a dial tone.

· Subject to multi-path distortion

Work Cited

Blume, Sherry, “3G Whiz”, Wireless Review, 29 February 2000.

Holt, Chuck, “Plug & Play; SIDEBAR”, Wireless Review, 29 February 2000.

Milstein, Laurence, “Waveform and Receiver Design Considerations on Wideband CDMA”, Personal Communications, Oct. 1999: 24.

Palenchar, Joseph, “Ericsson adds variety to line, including TDMA/CDPD phone”, Twice,

23 Aug 1999: 32-33.

“QUALCOMM Unveils Wireless Internet Strategy; - High Data Rate Technology Demonstrates Mobile Wireless Internet Access”, PR Newswire, 8 November 1999.

Zsigo, Konstantin J., “CDPD's Future”, Wireless Review, 1 April 1999.

http://www.qualcomm.com/cda/qcp/about_cdmaphones/0,1419,1_8,00.html#call_security

http://www.cdg.org/frame_tech.html

http://www.webproforum.com/tdma/topic02.html

http://www.webproforum.com/tdma/topic04.html