Difference Between Frequency Diversity and Time Diversity

Diversity is a well-known concept in the telecommunication industry. Generally, diversity refers to optimizing the signals by increasing the number of transmission channels. It is achieved by transmitting multiple copies of the same data. Moreover, frequency diversity and time diversity are two vital types of diversities to diminish the fading of the communication signal to enhance the signal quality between sender and receiver.

Frequency Diversity vs Time Diversity

The main difference between frequency diversity and time diversity is that frequency diversity means changing the frequency of the same signal or increasing the number of frequency carriers. On the other hand, time diversity means transmitting the same signal at a different time interval to avoid fading and disturbance in the signal.

Frequency Diversity vs Time Diversity

The frequency diversity technique is not so old since it was introduced in the 20th century. During that time, improvement in radio signal became a need to avoid disturbance in signals between sender and receiver. Therefore, expertise tried to modify the frequency of the same signal to reduce signal fading (amplitude variation).

Sometimes, disturbance or fading in a signal is experienced due to improper time management of the signals. The technique of time diversity means diverting the time of the same channel. The modified time interval must be higher than the coherence time ( when a problem arose in the data due to time).

Comparison Table Between Frequency Diversity and Time Diversity

Parameters of ComparisonFrequency DiversityTime Diversity
DefinitionFrequency diversity means diverting the frequency of the data sent.Time diversity means modifying the interval for disturbance-free data.
AmountThe frequency of the signal must be higher than the coherence bandwidth.The time interval of data should be more than the coherence time.
PreferencesSince we need spare bandwidth for the frequency diversity, it is preferred less.One does not need to install spare satellites to use time diversity.
ProcedureCertain frequency is assigned to each sender to transmit, and the receiver coordinates with that frequency level.A signal is divided into different time slots to avoid fading of it.
Example Frequency-hopping spread spectrum is an example of frequency diversity.An example of time diversity is the Rake receiver (a radio-based technique to combat data fading).

What is Frequency Diversity?

Frequency diversity is a vital technique in wireless networks systems (telecommunication, Wi-Fi signal, etcetera). Frequency diversity, as the name implies, is the process of diverting the frequency level to maintain the quality of networking communications.

The signal travels utilizing two or more carriers frequency in this technique ( measured in Hertz). It is suitable for line-of-sight propagation and belongs to the micro density group. Each signal is separated from the other based on frequency to diminish signal to noise ratio.

The level of frequency chosen should be more than that of coherence bandwidth ( a level of frequency at which the channel is flat or constant). This way, each transmitting signal will experience distinct waves and will not be co-related to one- another.

It aids the receiver in receiving signals from a variety of pathways. Frequency diversity is implemented via N:1 protection switching, according to experts.

Through the N number of the carrier frequency, one frequency is used to build a frequency diversity scheme. It means one spare bandwidth is required for frequency diversity.

A single antenna is necessary to boost the signal’s intensity through frequency diversity. Moreover, the number of receivers would be similar to the number of channels. It could be an expensive technique in size and power management.

What is Time Diversity?

Time diversity is also a crucial technique in the networking sector. It means sending the same information but at different time intervals. To put it another way, signals are sent out again at specific time slots.

Each of which must be longer than the time at which the signals faded earlier (coherence time). The sender sends the encoded signal with the forward error control coding. This technique is called channel coding to minimize the errors in signals.

Signal fading, interference from a transmitter, or obstacles between the sender and receiver can cause errors (error bursting). This technique is applied when more errors appeared at an interval of time, but the signals were excellent or less faulty at another time interval.
Moreover, a few or no hardware exists for error control. Through time diversity, users can recollect information that they missed due to signal error. An example is the Rake receiver in CDMA (Code Division Multiple Access).

Rake in English means collecting something. Rake receiver is practically helpful in combating signal error issues. It consists of sub receivers under CDMA.

When a sender sends data, but it runs into difficulties on the way, the signals pass through many routes to the rake receiver. Rake receiver flows the same signals from multiple sub receivers (fingers) at different time slots. It is how the receiver receives the error-free signal.

Main Differences Between Frequency Diversity and Time Diversity

  1. The term frequency diversity means modifying the frequency of the transmitting signal to avoid distortion. On the other hand, time diversity means changing the time of the transmitted data.
  2. The technique frequency diversity is expensive to remove the error from the signals. However, the time diversity method is cheap because less hardware is required for protecting data signals.
  3. The frequency diversity is less preferable technology as compared to the time diversity method.
  4. Senders are assigned with frequency to transmit the data, and receivers tune with them under the frequency diversity method. On the contrary, signals are divided into separate time intervals during transmission in the time diversity technique.
  5. The practical example of frequency diversity is the frequency hopping spread spectrum. However, in the case of time diversity, it is Rake receiver.

Conclusion

Wireless networking has become widespread in the world as a part of telecommunication. When people avail telecommunication services, the sender transmits the signals to the receiver. However, sometimes receiver is unable to receive the original data signal because it has been distorted. Moreover, transmitted signals fade due to noise and other such errors.

Frequency diversity and time diversity are two technologies that assist the receiver to have access to error-free signals. The transmission frequency increases to remove the unwanted noise under frequency diversity. On the other, data’s traveling time is bifurcated into different time slots to transmit the signal without any problem in the case of time diversity.

References

  1. https://dl.acm.org/doi/abs/10.1145/2030613.2030642
  2. https://ieeexplore.ieee.org/abstract/document/6513233/
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