Review: Preamble-based channel estimation in OFDM/OQAM systems: A review

TLDR: A review of the existing preamble structures and associated channel estimation methods is given, for both single- (SISO) and multiple-antenna (MIMO) systems.

About: This article is published in Signal Processing.The article was published on 2013-07-01 and is currently open access. It has received 157 citations till now. The article focuses on the topics: Orthogonal frequency-division multiplexing & MIMO.

Figures

Fig. 3. Preamble structures for (a) IAM-R , (b) IAM-I, (c) IAM-C methods, and E-IAM-C method for (d) EZ0 and (e) Eo0. M¼8. OQPSK modulation is assumed. d0 and d1 are randomly chosen BPSK symbols.

Fig. 6. Magnitude squared of the modulated IAM preambles. M¼512, K¼3. QPSK modulation.

Fig. 4. Preamble structures aiming at interference cancelation: (a) [43], (b) [51], (c) [91], and avoidance: (d) [42,25]. M¼8. OQPSK modulation is assumed.

Fig. 10. As in Fig. 8, for 2 2 MIMO systems.

Fig. 9. (a) As in Fig. 8(a), but with preamble powers equalized only at the SFB input. (b) Focus on (a), at the below 10 2 BER level.

Fig. 1. The first-order time-frequency neighborhood of FT point (p,q).

Frequently asked questions

Q1. What are the contributions in "Preamble-based channel estimation in ofdm/oqam systems_ a review" ?

This paper focuses on channel estimation for OFDM/OQAM systems based on a known preamble. 

Q2. Why is the focus on the middle non-zero preamble vector dropped?

Since the focus will be on the middle non-zero preamble vector in each antenna, the time index (normally q¼1) will be dropped for simplicity. 

Q3. How many complex symbols are required for training?

This implies that, for each subcarrier, (at least) 1.5 complex symbols are required for training, representing an increased (though not significantly) overhead compared to CP-OFDM. 

Q4. How can one use the pattern of interference cancelation to design a preamble?

One can, however, easily use it to design a preamble with the property of interference cancelation, by simply applying the above pattern for every third subcarrier and resorting to interpolation for the rest of them. 

Q5. What is the second approach to the interference approximation method?

The second one, interference approximation method (IAM), aims at approximating the intrinsic imaginary interference from neighboring pilots and hence constructing complex pseudo-pilots as above, to accommodate the complex CFR. 

Q6. Why do FBMC systems suffer from spectral leakage?

This is due to the fact that, although the subcarrier functions are perfectly time limited, they suffer from spectral leakage in the frequency domain and hence inter-carrier interference (ICI) results under non-ideal conditions. 

Q7. How many data symbols would be used to create a preamble?

This would result in a preamble containing about 4M=3 data symbols; this is a considerable gain in spectral efficiency compared to the methods previously described. 

Q8. How can one maximize the magnitude of the pseudo-pilots?

It can be verified from (6) that one can do better in maximizing the magnitude of the pseudo-pilots if imaginary pilot symbols Edp,1 of maximum modulus d are also allowed in the preamble.