CdmaOne Basics and Technical Details

CDMAOne is a 2G wireless technology that uses code division multiple access (CDMA) to provide digital cellular network services. It was first introduced in 1993.

CDMAOne operates on a single carrier frequency, which is divided into multiple channels to support multiple users. This allows for more efficient use of bandwidth.

CDMAOne uses a combination of spreading code and pseudorandom noise (PN) to encode and decode data. This process enables multiple users to share the same frequency band without interfering with each other.

CDMAOne has a maximum data rate of 14.4 kbps, which is relatively slow compared to modern wireless standards.

IS-95, also known as CDMAOne or cdmaOne, uses CDMA technology to separate mobile users within a cell by unique codes instead of unique frequency carriers.

This approach allows all cells in an area to use the same frequency carrier without interference, which was a major limitation of earlier systems like GSM and D-AMPS.

CDMAOne employs spread spectrum communication, specifically direct sequence spreading, which is also used in 3G CDMA2000 networks.

Digital transmission is a key feature of CDMAOne, significantly improving call quality and capacity compared to analog systems.

This digital transmission method allowed for a greater number of concurrent calls and users on the network.

CDMAOne also provided better security through digital transmission, making calls less susceptible to eavesdropping and interference.

CDMAOne was designed to be backward-compatible with analog AMPS systems, facilitating a smooth transition from analog to digital technologies.

The IS-95 standards describe an air interface, a set of protocols used between mobile units and the network. This air interface is structured as a three-layer stack, which is a key characteristic of the CDMAOne technology.

The L1 layer corresponds to the physical (PHY) layer, which is the foundation of the protocol stack. It's responsible for transmitting and receiving data between the mobile unit and the network.

L2 refers to the Media Access Control (MAC) and Link-Access Control (LAC) sublayers, which work together to manage data transmission and control access to the network.

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The first protocol revision of cdmaOne was developed under an ANSI standards process as P_REV=1, which was published in 1995 as J-STD-008 for the North American PCS band.

P_REV=1 was defined for the North American PCS band, but a similar version, IS-95, was developed under the TIA standards process for the North American cellular band, offering interoperation with the analog cellular network.

IS-95 and J-STD-008 have most technical details in common, reflecting the immature style and structure of the documents due to Qualcomm's internal project being standardized.

P_REV=2 is termed Interim Standard 95A (IS-95A), developed for Band Class 0 only as an incremental improvement over IS-95 in the TIA standards process.

P_REV=3 is termed Technical Services Bulletin 74 (TSB-74), the next incremental improvement over IS-95A in the TIA standards process.

P_REV=4 is termed Interim Standard 95B (IS-95B) Phase I, and P_REV=5 is termed Interim Standard 95B (IS-95B) Phase II, which provided for a merging of the TIA and ANSI standards tracks under the TIA and interoperation of IS-95 mobile handsets in both band classes.

P_REV=4 was the most popular variant of IS-95, with P_REV=5 seeing minimal uptake, mainly in South Korea.

P_REV=6 and beyond fall under the CDMA2000 umbrella, with technical improvements and a more mature layout and content, providing backwards-compatibility to IS-95.

The IS-95 standards describe a three-layer stack, where L1 corresponds to the physical (PHY) layer, L2 refers to the Media Access Control (MAC) and Link-Access Control (LAC) sublayers, and L3 to the call-processing state machine.

The air interface is a key part of the IS-95 standards, used between mobile units and the network.

This three-layer stack provides a clear and organized framework for understanding the IS-95 protocols.

The physical (PHY) layer, or L1, is the foundation of the IS-95 stack, responsible for transmitting and receiving data.

The Media Access Control (MAC) and Link-Access Control (LAC) sublayers, or L2, work together to manage data transmission and control the link.

The call-processing state machine, or L3, is the top layer of the IS-95 stack, handling call processing and state management.

The Physical Layer of CDMAOne is where the magic happens, folks! Radio signals are transmitted in both the forward and reverse directions, with base stations (BTS's) handling the forward transmissions.

Every BTS is synchronized with a GPS receiver, ensuring tightly controlled transmissions in time. This synchronization is crucial for maintaining the integrity of the signal.

In the forward direction, QPSK is used with a chip rate of 1,228,800 per second. Each signal is spread with a Walsh code of length 64 and a pseudo-random noise code (PN code) of length 2, resulting in a PN roll-over period of 803 ms.

For the reverse direction, radio signals are transmitted by the mobile, using OQPSK to operate within the optimal range of the mobile's power amplifier. The chip rate remains the same, 1,228,800 per second, with signals spread using Walsh codes and the pseudo-random noise code.

The physical layer is the foundation of the IS-95 system, and it's responsible for transmitting signals between the network and mobile devices.

Radio signals are transmitted by base stations in the forward direction, and these signals are tightly controlled in time thanks to a GPS receiver.

Every BTS transmission is QPSK with a chip rate of 1,228,800 per second, and each signal is spread with a Walsh code of length 64 and a pseudo-random noise code of length 2.

The reverse direction sees radio signals transmitted by the mobile, which are OQPSK in order to operate in the optimal range of the mobile's power amplifier.

The chip rate for both forward and reverse link transmissions is 1,228,800 per second, and signals are spread with Walsh codes and pseudo-random noise codes.

Paging channels are transmitted by BTSs, with at least one and as many as seven channels starting with Walsh code 1.

The paging channel frame time is 20 ms, and it's time aligned to the IS-95 system 2-second roll-over.

Two possible rates are used on the paging channel: 4800 bit/s or 9600 bit/s, both encoded to 19200 symbols per second.

In the world of digital communications, the physical layer is where the magic happens. A key component of this layer is the block interleaver, which plays a crucial role in ensuring the integrity of the data being transmitted.

A block interleaver is essentially a 24 by 16 array that rearranges the symbols sent after convolution coding and repetition. This process helps to spread the data across the array, making it more resistant to errors.

The block interleaver is a 20 ms device, which means it operates within a specific time frame to optimize data transmission. This is just one of the many ways the physical layer ensures that data is transmitted efficiently and accurately.

The forward channels in CDMAOne are a crucial part of the network, allowing data to be transmitted from the network to mobiles.

Every BTS dedicates a significant amount of output power to a pilot channel, which is an unmodulated PN sequence, or spread with Walsh code 0. Each BTS sector in the network is assigned a PN offset in steps of 64 chips.

The pilot channel allows mobiles to determine system timing and distinguish different BTSs for handoff, with its strong autocorrelation function.

Data is carried on other forward channels, selected by their Walsh code, and consists of network signaling and user traffic. Data is divided into frames of bits, which are then passed through a convolutional encoder, adding forward error correction redundancy.

A BTS transmits a sync channel spread with Walsh code 32, which continually transmits a single message, the Sync Channel Message. The sync channel frame is 803 ms long, and its frame boundary is aligned to the pilot.

The sync channel message contains information about the network, including the PN offset used by the BTS sector.

The paging channel contains signaling messages transmitted from the network to all idle mobiles, circulating network overhead information while the paging channel is free.

Here's a summary of the forward channels:

The forward traffic channel carries individual voice and data calls supported by IS-95, with a frame time of 20ms.

The IS-95 standards describe an air interface, a set of protocols used between mobile units and the network, as a three-layer stack: L1 for the physical layer, L2 for Media Access Control (MAC) and Link-Access Control (LAC) sublayers, and L3 for the call-processing state machine.

IS-95 uses a full-duplex scheme called Frequency Division Duplex (FDD), which means separate frequency bands for the forward and the reverse links.

There are two bands in IS-95; the 850 MHz band and the 1900 MHz band.

In the 850 MHz band, the reverse link is from 824 MHz to 849 MHz, while the forward link is from 869 MHz to 894 MHz.

The separation between the starting frequencies for reverse and forward links is 45 MHz.

In the 1900 MHz band, the separation is 80 MHz, so the reverse link is from 1850 MHz to 1910 MHz, while the forward link is 1930 MHz to 1990 MHz.

The table below summarises the forward and reverse link frequencies in IS-95 (cdmaOne).

IS-95 has a carrier bandwidth of 1.25 MHz to enable peak download data rates of up to 14.4 kbps using IS-95 A and up to 115 kbps using the enhanced version, IS-95 B.

IS-95 offers capacity advantages due to its ability to accommodate more users per MHz.

CDMAOne vs CDMA2000: What's the Difference?

CDMAOne and CDMA2000 are two different wireless technologies that were developed by Qualcomm. CDMAOne was the first commercial CDMA technology, released in 1995.

CDMAOne supported data rates of up to 14.4 kbps, which was relatively fast for its time.

CDMA2000, on the other hand, was released in 2000 and offered significantly faster data rates of up to 2.4 Mbps.

CDMA2000 also supported higher voice capacity and better coverage than CDMAOne.

The key difference between CDMAOne and CDMA2000 is the level of 3G capabilities. CDMA2000 was designed to be a 3G technology, while CDMAOne was a 2G technology.

CDMAOne was standardized in 1993 by the International Telecommunication Union (ITU) as IS-95.

This marked a significant milestone in the development of digital cellular services. CDMAOne was designed to coexist with analog AMPS networks, which were still prevalent at the time.

CDMAOne offered better call quality and security compared to analog systems like AMPS. It was particularly useful in regions where analog systems were dominant, such as the United States and parts of South America.

CDMAOne paved the way for more advanced CDMA technologies. Its successors include CDMA2000, which introduced higher data rates and improved performance.

CDMA2000 further evolved into various standards like 1xRTT and EV-DO. These advancements built upon the foundation established by CDMAOne, enabling faster and more reliable data transmission.

Testing and deployment of cdmaOne base station equipment requires specialized tools and techniques to ensure peak performance. These modern testers provide clear insight into complex transmitter systems by capturing and displaying information in formats that are easy to interpret.

Leading edge troubleshooting tools and techniques are essential to the maintenance of systems at peak performance. They must be compact, dependable, and rugged to withstand the rigors of field use.

Network systems must perform reliably in the face of fierce competition – success or failure will be the direct result of customer satisfaction. Exponential growth in other wireless and RF devices is introducing new sources of noise and interference that threaten to degrade performance.

Testing BTS RF signals is crucial for maintaining a reliable and efficient wireless communication system. The stakes are high, as network systems must perform reliably in the face of fierce competition.

A cdmaOne transmission looks like a complex combination of data, spread and combined for transmission, and then modulated onto an RF carrier with a channel bandwidth of 1.2288 MHz. This is a critical aspect to understand when testing BTS RF signals.

Traditional measurement tools specified for cdmaOne standards include a spectrum analyzer, a power meter, a mobile station simulator, and a waveform-quality/code-domain power measurement device. These tools are essential for checking the RF signal performance of a BTS transmitter.

A spectrum analyzer is used to examine the frequency domain picture of a cdmaOne BTS transmission, while a power meter measures the power of the RF signal. These tools are critical for ensuring that the BTS transmitter is operating within specifications.

The code domain picture of a cdmaOne BTS transmission is simply the demodulated data from the frequency domain picture. This is an important concept to grasp when troubleshooting issues with BTS RF signals.

The cdmaOne standards specify the use of these traditional measurement tools to ensure that BTS transmitters are operating correctly. By using these tools, technicians can quickly identify and troubleshoot problems with the RF signal.

Deployment is a critical step in the testing and deployment process. cdmaOne was used in North America, Japan, and South Korea, where 2G GSM is not available.

In Hong Kong, Hutchison Telecom used cdmaOne, although other operators and Hutchison Telecom itself also provided GSM services.

Here's a list of the regions where cdmaOne was used:

CDMAOne is often compared to other wireless technologies, but one notable comparison is with GSM. GSM had a similar capacity to CDMAOne, but with a smaller cell size.

CDMAOne also had a higher capacity than TDMA, which was another wireless technology used during the same time period. This allowed CDMAOne to support more users and data traffic.

However, CDMAOne had a lower capacity than 3G technologies, which were introduced later and offered faster data speeds and higher capacity.

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CdmaOne's capacity is impressive, thanks to its use of CDMA techniques. It has a fixed bandwidth, but takes active steps to improve signal-to-noise ratio (SNR).

This is made possible by the variable-rate nature of traffic channels, which provide lower-rate frames to be transmitted at lower power, causing less noise for other signals. Signals that are not correlated with the channel of interest appear as noise, and signals carried on other Walsh codes are essentially removed in the de-spreading process.

Active power control is also used on the forward traffic channels, where the mobile sends signaling messages to the network indicating the quality of the signal. The network then controls the transmitted power of the traffic channel to keep the signal quality just good enough.

As a result, CdmaOne can squeeze more users into the same radio spectrum, providing an inherently lower noise level than other cellular technologies. This is a significant advantage in densely populated areas.

Here's a breakdown of the key factors that contribute to CdmaOne's capacity:

These factors combined enable CdmaOne to support a large number of users while maintaining a high level of performance.