CDMA Essay Example | Topics and Well Written Essays - 750 words

CDMA - Essay Example Soft handover capabilities are offered to improve the voice quality whereas a RAKE receiver is used to reduce the effect of multi-path fading. J-STD-008 is the PCS version of IS-95; both were combined to IS-95B. Modulation is a process by which the characteristics of a sinusoidal carrier waveform are modified using values of coded symbols that represent the original message. Once the carrier waveform is modulated, it carries the message along to the receiver, where demodulation will reverse the process and extract the original message from the carrier. In the CDMA (IS-95) cellular system, Binary phase shift keying (BPSK) modulation is used on the forward link. Using algebraic notations, we can mathematically express a carrier wave with certain phase shift applied as the sum of a cosine or I(t) and a sine or Q(t) wave component. I(t) and Q(t) , or simply I and Q, are called the real (in phase) and the imaginary (quadrature-phase)data components respectively. This representation is not simply an algebraic identity; it also provides the required base for the necessary modulation and demodulation operations. With this representation we have two superimposed binary PSK waveforms. It is easier to modulate and demodulate such waveforms. The waves are generated by the transmitter at the same frequency, and then each of the components is modulated by 0 or 180 degrees phase shifting (detecting 180 degrees phase shifts is easier than detecting 90 degrees phase shifts). After that the components are summed together and transmitted. Once the s ignal arrives at the receiver, the receiver will generate two reference waveforms for the demodulation process to be carried out. A 64-ary orthogonal modulation scheme using Walsh words are employed on the reverse link. This conveys 6 coded symbols per each Walsh word. Note that "Walsh words are groups of 2N vectors or words which contain 2N binary elements which with them selves and their logical inverses form a mutually orthogonal set."(Ernest) phase modulation remains the form of change the carrier will undergo. This means that a Walsh word w(t) with binary chips 1 will be multiplied by the carrier to mathematically produce either a positive or a negative version. The effect of the Walsh word will be to shift the phase of the negative version by 180 degrees, while the positive version will be shifted by 0 degrees (which means that it will be left intact). The mobile determines the data bit on the forward link by simply examining all the received Walsh chips and checking if they are all either inverted or not relative to the chip values assigned to it. The base station will also recognize the 1 pattern of the transmitted Walsh word using the fast Walsh transform (FWT) on the reverse link. In this process, the 1 pattern received will be compared with all possible 64 Walsh words. RAKE RECEIVER CDMA spreading codes are different than other conventional modulation schemes. They are designed to offer extremely low correlation between successive chips. As a result, the effects of the channels propagation delay spread are merely multiple versions of the original signal. If such multipath components experience a time large time delay compared to the chip duration. They will be discarded as uncorrelated noise by the CDMA receiver. This happens because the uncorrelated noise will be made negligible by the spread spectrum processing gain after

DX wk 8 Essay Example | Topics and Well Written Essays - 1250 words

DX wk 8 - Essay Example Also, the episode of bulimia does not have to be done in one place. As an example, the individual can start when they are at a restaurant and finish when they get home (American Psychiatric Association, 2000). Bulimia also has two subtypes: Purging, in which the individual induces vomiting after eating or the non-purging type. In purging, the individual misuses laxatives, diuretics, or enemas in their most current episode. In the non-purging type, the individual misuses laxatives, diuretics or enemas but they do not purge afterward (American Psychiatric Association, 2000). In contrast, Binge-Eating Disorder (BED) has recurrent eating binges but they do not purge afterwards (Nevid, Rathus and Greene, 2005). BED is usually occurring in obese individuals and is often associated with long-term attempts to lose weight; they also experience depression. In BN, the individual is usually thin and vomiting to stop from getting fat. I believe that EDNOS is more often diagnosed because there can be gray areas when dealing with eating disorders and because there needs to be a history of certain types of behavior. Generally, the counselor must do an interview with the individual and they must be able to give the counselor this history. Also, when there are specific factors that look like BN or Anorexia, but all the criteria is not met, ENOS can be the better diagnosis. As an example, an individual may have all the characteristics of AN but they still have a normal weight (American Psychiatric Association, 2000). This also may be a "safer" diagnosis critically when the clinician does not have enough medical history. Mr. A has come to counseling because he enjoys dressing as a woman. He has his own wardrobe and makeup and he belongs to a networking group in his area. Also, Mr. A may be experiencing depression so the clinician should talk to him more about this depression to determine whether it is clinical or