The resulting down-converted CDMA signal is finally processed by a digital signal processor 6 a within the mobile modem 6. The modem 6 also generates a baseband CDMA signal for transmission, required for CDMA telecommunication operation , this signal is up-converted to the higher frequency range required for transmission by an IF to RF up-converter 5 which drives an RF power amplifier 4.
This power amplifier 4 feeds the signal into the duplexer 2 that then passes the signal to the antenna 1 for broadcast. When operating in GPS mode, transmit functions are optionally dependent on how the telecommunications service provider integrates GPS into their system.
The manufacturing costs may be reduced by decreasing the number of components, and hence cost, can be saved if the GPS signal is passed through the standard CDMA channel select filter 10 , shown in FIG. This filter has a typical bandwidth of 1. Manufacturers, e.
Qualcomm, have indicated that new modems will support GPS signal decoding. Thus, a first order estimate of losses due to reduced bandwidth can be 10 log 1. This loss of code power is small compared to that encountered in some GPS implementations, e. A RF down-converter 9 receives the output of the signal path selector 15 and a local oscillator signal A intermediate frequency IF channel select filter 10 further filters the output of the down converter prior to additional signal conditioning not shown the resultant signals are then sent to a baseband processor not shown to recover the CDMA telecommunication signals or GPS data as required.
The selected signal is converted to the intermediate frequency, by the appropriate local oscillator input 16 to the RF down-converter 9 , and passed through the IF channel select filter In addition, the same control signal may control the signal path selector When CDMA operation is compared with GPS, the average current required can be less as the system swaps between the two low noise amplifiers.
Where the telecommunication mobile station uses a high dynamic range LNA, e. The signal path selector 15 may be implemented in several ways. The signal path selector 15 may alternatively be a circulator, a coupler, phased line lengths that use the out of band impedance characteristics of the filters to transform the effective loading at a junction point, a duplexer, or a diplexer that substitutes or incorporates the filtering functions 8 and In each embodiment, the principle of routing the desired signal along a path to the required point is the same.
When the signal path selector 15 is implemented, the main requirement will be to minimize losses before the downconverter 9 such that the CDMA mobile station sensitivity and dynamic range are optimized for a given CDMA-LNA 7 gain. The positions of the signal path selector 15 and the telecommunications down-converter 9 have been transposed, compared to the first embodiment. A LO path switch 18 interposes the LO signal 16 and the down-converter 9.
It is noted that the LO switch 18 could be implemented as part of the CDMA section as shown or part of the GPS section, or as a separate switch function external to either section. In any of these configurations the principle is the same. Throughout these diagrams only a single connecting line is shown, for clarity. Also mixers of the single sideband form, commonly known as image reject mixers, may be used at 9 and 17 to eliminate or minimise the filtering functions 8 and The use of such devices does not change the general principle used in this description.
It will be evident to those skilled in the art that the frequency plans given in FIGS. Also, that other frequency plans can be used to give the same final IF frequencies. In FIGS. Multiple band antennas are well documented in prior art as are antenna network switch solutions.
What is claimed is: 1. A CDMA mobile station comprising:. A CDMA mobile station, as defined claim 1 , wherein one of the duplexer, band select filter, and the first and second filters of the GPS section is selected from a group that includes thin film bulk acoustic wave resonator filters, ceramic filters, and surface acoustic wave filters.
A CDMA mobile station, as defined in claim 1 , wherein the switch is selected from a group that includes a mechanical switch, a semiconductor switch, a duplexer, a diplexer, a coupler, a circulator, and phased line lengths.
A CDMA mobile station, as defined in claim 1 , wherein the band select filter is a filter having a passband greater than 1.
First, we have assumed that all the chips are synchronized in time. In reality, doing so is impossible. What can be done is that sender and receiver synchronize by having the sender transmit a long enough known chip sequence that the receiver can lock onto. All the other unsynchronized transmissions are seen as random noise. The longer the chip sequence the higher is the probability of detecting in presence of noise.
For extra security, bit sequences can use error correcting codes. Chip sequences never use error correcting codes. For each channel the base station generates a unique code that changes for every connection. The pseudo-random code must have the following properties:. It must be deterministic. The subscriber station must be able to independently generate the code that matches the base station code.
It must appear random to a listener without prior knowledge of the code i. The cross-correlation between any two codes must be small see below for more information on code correlation. The code must have a long period i. In this context, correlation has a specific mathematical meaning.
In general the correlation function has these properties:. Intermediate values indicate how much the codes have in common. The more they have in common, the harder it is for the receiver to extract the appropriate signal. There are two correlation functions:. The receiver uses cross-correlation to separate the appropriate signal from signals meant for other receivers, and auto-correlation to reject multi-path interference.
Some terminology related to the pseudo-random code:. Transmitting Data. QPSK uses four different states to encode each symbol. The four states are phase shifts of the carrier spaced 90degrees apart.
By convention, the phase shifts are 45, , , and degrees. Since there are four possible states used to encode binary information, each state represents two bits. Algebraically, a carrier wave with an applied phase shift, Y t , can be expressed as a sum of two components, a Cosine wave and a Sine wave, as:.
I t is called the real, or In-phase, component of the data, and Q t is called the imaginary, or Quadrature-phase, component of the data. We end up with two Binary PSK waves superimposed. These are easier to modulate and later demodulate. The transmitter generates two carrier waves of the same frequency, a sine and cosine. I t and Q t are binary, modulating each component by phase shifting it either 0 or degrees.
Both components are then summed together. The receiver generates the two reference waves, and demodulates each component. It is easier to detect degrees phase shifts than 90degrees phase shifts. The following table summarizes this modulation scheme. Note that I and Q are normalized to 1. In order to make full use of the efficiency of Digital Signal Processing, the conversion of the Information data into complex symbols occurs before the modulation.
To spread the Information data the system performs complex multiplication between the complex PN codes and the complex data.
Many channels are added together and transmitted simultaneously. This addition happens digitally at the chip rate. Since I and Q are no longer limited to 1 or -1, the phase shift of the composite carrier is not limited to the four states, the phase and amplitude vary as. Since the PN-code has the statistical properties of random noise, it averages to zero over long periods of time such as the symbol period.
Therefore, fluctuations in I and Q, and hence the phase modulation of the carrier, that occur at the chip frequency, average to zero. Over the symbol period the modulation averages to one of the four states of QPSK, which determine what the symbol is. The receiver performs the following steps to extract the Information:. The receiver generates two reference waves, a Cosine wave and a Sine wave. What is the full form of RTT?
The traffic in a telecommunication network is measured by an internationally accepted unit of traffic intensity. Select the correct option.
The capacity of a cellular system in fixed area is directly proportional to which of the following? The main objective of CELL in a cellular mobile system is. An instrument used to measure ones location in terms of coordinates. Suggested Test Series. More Communication Systems Questions Q1. Consider the following statements: a. The speed of telecommunication satellite relative to earth is zero. Hence it appears to be stationary to a person on the earth.
Which of the following Pulse time Modulation does not exist in practice? The frequency which is not transmitted in AM transmission is. In a communication satellite, the telephone channels are assembled in. In television transmission, the type of modulation used for video is.
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