Milestones:Development of CDMA for Cellular Communications, 1989

Title

Development of CDMA for Cellular Communications, 1989

Citation

On 7 November 1989, Qualcomm publicly demonstrated a digital cellular radio system based on Code Division Multiple Access (CDMA) spread spectrum technology, which increased capacity, improved service quality, and extended battery life. This formed the basis for IS-95 second-generation standards and third-generation broadband standards that were applied to cellular mobile devices worldwide.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

32.895146, -117.19773, In the vicinity of the main entrance or the main lobby of the headquarters of Qualcomm, Inc., at 5775 Morehouse Drive, San Diego, CA 92121 USA (32.895146 °N -117.19773°W)

Details of the physical location of the plaque

TBD, but in the vicinity of the main entrance or the main lobby of the headquarters of Qualcomm, Inc., at 5775 Morehouse Drive, San Diego, CA 92121 USA

How the intended plaque site is protected/secured

The main entrance and the main lobby of the headquarters of Qualcomm, Inc., at 5775 Morehouse Drive, San Diego, CA 92121 USA, are fully accessible to the public.

Historical significance of the work

First Generation (1G) Analog Cellular Networks In the 1980s, mobile systems managed network access by assigning specific frequency channels to users. In the first generation of cellular (now known as “1G”), one user would occupy a single channel when making a cellular call, thus limiting the capacity of a given cell to the number of channels available within a cell site.

Second Generation (2G) Digital Cellular Networks In the late 1980s, the ability to service multiple subscribers within a single channel was accomplished in the second generation of cellular (“2G”) with a technology called time division multiple access (TDMA). In this technique, a radio channel was divided into time slots and assigned to multiple users. Within an assigned time slot, only a single user utilized the channel. However, the switching across time slots was done so quickly that users didn’t notice that the communication channel was shared.

In the North American 2G standard (called D-AMPS, or Digital AMPS), three users occupied a 30 KHz channel. GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), the European 2G technology initiated by the European Telecommunications Standards Institute (ETSI) standards body, also utilized TDMA but with a wider 200 KHz channel supporting up to eight users.

Additionally, because neighboring cells were on different frequencies (to prevent interference), a “hard” switch in frequencies occurred when moving from one cell to the next. This hard switch (known as a hard handover) caused intermittent dropped calls and problems with users “ping ponging” between base stations. In addition, as demand for mobile services continued to grow, it become clear that the capacity gains of the TDMA approach would not be able to scale to accommodate future growth.

Code Division Multiple Access (CDMA) CDMA, which was historically used for military communications, is a technology in which signals are spread over a frequency using a unique code for each signal, and the resulting low-power signals travel over the same frequency at the same time. At the receiver, the signal is reconstructed using the same unique code that was used for spreading. The desired signal is separated out from the rest of the signals, which are received, but being received as background noise they can be effectively minimal until a certain level.

When they were in use, CDMA networks utilized all the available spectrum by spreading user traffic across a channel, reducing the traditional guard bands frequency required with TDMA. Multiple users were thus able to communicate simultaneously over the same frequency.

As dead time (silence) makes up over half of a typical telephone conversation, CDMA’s suppression of the transmission of silence greatly increased energy and capacity efficiency. Because CDMA was a spread spectrum technology, system capacity directly benefited from efficiencies realized within the communication channel.

Variable rate coding (VRC) introduced four rates of transmission, (9600, 4800, 2400, and 1200 bits per second (bps)), allowing a cellular device to throttle the rate of transmission depending on the level speech activity. [2] Dead time would be transmitted at 1200 bps, greatly reducing the power and processing required for transmit and receive. Overall capacity increased by a factor of 3 with VRC. Additionally, the suppression of background noise (common in cellular communications at the time) greatly improving call quality. [3]

CDMA’s Impact on 3G CDMA’s benefits over TDMA included fewer dropped calls during handovers, higher capacity and bandwidth, improved voice clarity, lower device costs and longer battery life. Because of all of these benefits and more, all third generation cellular technical standards (“3G”) were based on the CDMA technology pioneered by Qualcomm. 3G ushered in the era of power efficient, low cost smartphones with internet access speeds that rivaled typical home internet access speeds.

CDMA thus created a technology foundation whose benefits have spanned many aspects of society, both economically and socially. Over half of the population now owns a mobile device, providing internet access to much of the world’s underserved communities. CDMA was the catalyst of this change.

As of 2016, there were around 3 billion 3G devices worldwide. This is shown, for example, in a chart showing 2G, 3G and 4G LTE presence in the world over time that can be found in a Working Document created for the European Union's European Parliament here: http://eur-lex.europa.eu/legal-content/en/TXT/?uri=CELEX:52016SC0306 (on p. 8 of the PDF here: http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52016SC0306&from=en).

Features that set this work apart from similar achievements

As described above, CDMA was radically different from competing solutions based on TDMA. Here is a list of distinguishing features brought to market by Qualcomm’s CDMA technology:

Soft Handoff A handoff scheme in which a new cell-site established service while the neighboring cell-site continued to service the call. When the mobile unit was located in the transition region, between the two cell-sites, the call would be switched back and forth between cell-sites as signal strength dictates without call interruption. Since the mobile unit was always communicating through at least one cell-site, no disrupting effects to the mobile unit or in service occurred. [11]

Once communications were firmly established with the new cell-site, the old cell-site discontinued servicing the call. The soft handoff was in essence a make-before-break switching function. In contrast, conventional cellular telephone systems were considered a break-before-make switching function.

Variable Rate Vocoder Speech signal compression through variable rate coding of frames of digitized speech samples. The level of speech activity for each frame was determined and an output data packet rate was selected from a set of rates based upon the determined level of frame speech activity.

The lowest rate of the set of rates corresponded to a minimum level of speech activity, such as background noise or pauses in speech, while a highest rate corresponded to a maximum level of speech activity, such as active speech. [2]

Power Control and Pilot A power control system that controlled transmission signal power for each cellular mobile telephone within cellular mobile system. The cell-site transmitted pilot was measured as received at the cellular device. Transmission power is then adjusted at the mobile unit in an opposite manner with respect to increases and decreases in received signal power. [9], [10]

Additionally, the system included a cell-site initiated power control mechanism where the cellular device’s transmitted power was measured as it is received at the cell-site. The cell-site could then transmit a command to the mobile unit to further adjust the mobile unit transmitter power. The feedback scheme was used to further adjust the mobile unit transmitter power so it arrived at the cell-site at a desired power level.

Significant references

[1] U.S. Patent: 4,901,307, "Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial,” K. Gilhousen, I. Jacobs, L. Weaver; priority date: Oct 17, 1986, issued: February 13, 1990.

[2] U.S. Patent 5,657,420, “Variable Rate Vocoder,” P. Jacobs, W. Gardner, C. Lee, K. Gilhousen, K. Lam, M. Tsai; priority date: June 11, 1991, issued: August 12, 1997.

[3] Dave Mock, The Qualcomm Equation, How a Fledgling Telecom Company Forged a New Path to Big Profits and Market Dominance, Chapter 5: “Disrupting the Cellular Status Quo Qualcomm Goes to Bat, 1989,” Anacom, 2005, pp. 68-69. Available at http://tinyurl.com/hk94yyn

[4] New York Times, TECHNOLOGY: "Holy War" Over the Future of Wireless, February 15, 1999.

[5] Journal IEEE Internet Computing, George Gilder on the Bandwidth of Plenty, January 1997, pp. 9-18.

[6] Wall Street Journal, Jacob’s Patter – An Inventor’s Promise Has Companies Taking Big Cellular Gamble – Qualcomm Boss’s Innovation In Digital-Phone System Is Problematic – and Late – Are Claims Hope or Hype?, September 6, 1996.

[7] IEEE Spectrum, 25 April 2013, Irwin Jacobs: Captain of CDMA - Qualcomm cofounder Irwin M. Jacobs wins the 2013 IEEE Medal of Honor for his pioneering work in digital communications - http://spectrum.ieee.org/geek-life/profiles/irwin-jacobs-captain-of-cdma

[8] Qualcomm Website: http://www.qualcomm.com/company/about/history - History: 1989 - Qualcomm makes a historic phone call, CDMA is proven.

[9] U.S. Patent 5,056,109, “Controlling Transmission Power in a CDMA Cellular Mobile Telephone System,” K. Gilhousen, R. Padovani, C. Wheatley; priority date: November 7, 1989, issued: October 8, 1991.

[10] U.S. Patent 5,257,283, “Spread spectrum transmitter power control method and system,” K. Gilhousen, R. Padovani, C. Wheatley; priority date: November 7, 1989, issued: October 26, 1993.

[11] U.S. Patent 5,101,501, “Providing a Soft Handoff in a CDMA Cellular Telephone System,” K. Gilhousen, R. Padovani, C. Wheatley; priority date: November 7, 1989, issued: March 31, 1992.

Supporting materials

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