You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Body-Centric Wireless Communications: A Survey of Hearing-Instrument Antennas 
Chapter Title:  I. INTRODUCTION 
1. Abstract of Cited Paper (BIB001):  The impact of antenna polarization on the ear-to-ear transmission channel at 2.45 GHz is investigated. Two antenna configurations have been considered for monopole antennas operated on small ground planes that are placed next to the human head. The two setups provide different current distributions on the ground planes, which has a drastic impact on the antenna polarization. Their performances are compared in terms of maximum path gain (|S 21 |) and obtainable bandwidth of the antenna structures. 
2. Abstract of Cited Paper (BIB002):  The effect of the anatomical variation of the head on the ear-to-ear communication at 2.45 GHz has been investigated. Several anatomical characteristics of the head, such as the dimensions and the position of the ears, have been recorded for a group of 25 test persons. Active Packet Error Rate (PER) measurements have been made by the use of digital Hearing Instruments (HI) as small wireless platforms in both indoor and outdoor environments. Two fundamentally different antenna configurations are compared. It is found that there is an effect of the distances over-the-top, around-the-front and aroundthe-back on the PER, due to constructive and destructive interference between surface waves that propagate along the different paths. The effect is different for the two different antenna types.

Literature Review:
Body-centric wireless communications have received much attention in the literature in recent years. This is due to the rise of small body-worn devices, which need to communicate wirelessly in order to offer improved functionality to the user. The Industrial, Scientific and Medical (ISM) band at 2.4 GHz is license free worldwide, and is therefore used to enable many Wireless Body Area Network (WBAN) applications. Additionally, all modern mobile phones are already equipped to communicate at 2.4 GHz by the use of the widespread Bluetooth ® protocol. Hearing Instruments (HIs) are a good example of such small body-worn devices that have become increasingly advanced in recent years. Modern top-line HIs are thus expected to be able to communicate wirelessly with mobile accessories, such as audio streamers and mobile phones. Furthermore, the binaurally fitted HIs are needed to communicate wirelessly with each other, ear-to-ear, in order to synchronize the amplification settings between the HIs. Further, it is possible to obtain audiological advantages, which, e.g. eases conversation in noisy areas. In order to conserve power, the accessorylink and the ear-to-ear link need to utilize the same radio and antenna. The challenge in using 2.4 GHz is that the head is lossy at these frequencies, with a skin depth δ s ≈ 21 mm. Therefore, the energy cannot propagate through the head. Instead the energy propagates around the head as creeping waves BIB001 , BIB002 . In this presentation, the characteristics of the ear-to-ear onbody propagation will be surveyed. Additionally, some of the many examples of HI antennas found in the literature will be reviewed, e.g., BIB003 -  , which are antennas that are suitable for use in small ear-worn devices.