The phrase "a coherence interval" is correct and usable in written English.
It can be used in contexts related to linguistics, communication, or data analysis, where it refers to a period or range in which coherence is maintained.
Example: "In analyzing the conversation, we found that a coherence interval of five seconds allowed for better understanding between the speakers."
Alternatives: "a consistency period" or "a coherence span".
Hence, for the equipath position for the addition of two beams, a coherence interval is defined as the separation of two points such that the absolute value |γ12(0)| is some prechosen value, usually zero.
Here, we assume that the variation of channel vectors during a coherence interval is ignorable.
From Figure1, a coherence interval is organized in three phases: uplink channel estimation period, uplink data transmission period, and downlink data transmission period.
Since h k changes over coherence intervals, without loss of generality, we take the communication between the BS and users in a coherence interval as an example for deeper analysis.
Especially as our methods can be conducted off-line, the computation complexity is not an issue in the real-time channel rank detection and channel estimation within a coherence interval of the channel.
We assume channel obeys reciprocity in TDD, i.e., the channel factors are the same for both the uplink and downlink, and h k remains constant during a coherence interval of length T. The transmission scheme of a conventional massive MIMO system with orthogonal pilots is shown in Figure1, where τ op (τ op ≥ K) and D op respectively represent the length of pilot and downlink data.
Further discussion on performance verifies the superiority of our proposed pilot design for high or low signal-to-noise-ratios (SNRs) with any coherence interval length.
And particularly for low or high SNRs with any coherence interval length, the superiority of our proposed pilot design is theoretically proven.
This corresponds to 576 bits to be sent by each user equipment within an arbitrary channel coherence interval.
For smaller values of the coherence interval, a small number of users is optimal so that not much of the coherence interval gets consumed in feedback.
Then the k th user's uplink achievable rate when the k1th k1 > k) user transmits a pilot in the first coherence interval is R k, 1 u k 1 = log 2 1 + ρ u M + 1 σ k, 1 2 ρ u ∑ t = 1 k 1 - 1 β t - ρ u σ k, 1 2 + ρ p β k 1 + 1. (41).
