A plan to relax investment restrictions on the State-backed 4-trillion-yuan ($621 billion) housing fund will boost bond trading and help cap yields, according to Guotai Junan Securities Co. The housing provident fund, which manages the money of Chinese workers saving to buy a house or apartment, will be allowed to invest in certificates of deposit, bonds of local governments and policy banks and other products approved by the management committee. It already invests in sovereign notes.